Ranger IAC question

[hermitjohn]

1994 4.0L.   Ok, last time to town once engine hot, have low idle and it will stall.  Restart, but have to feather the pedal.   Ok, doing google, I get crazy amount of possibilities from Ranger owners.  I can see the IAC or the TPS.  The rest.... eh, who knows.

Anyway I just removed the IAC and with it plugged in and ignition on, but negative battery cable off, I put the battery cable back on while observing.  The little plunger thingie moves, stays there a second or two, then returns to home position.  Is this what it is supposed to do?

Just for giggles, I also tried removing the MAF sensor harness connector with engine running.  Absolutely no difference.  Online some people saying their Ranger dies when they do this.  Others where it makes no difference, like mine.  Apparently it has a limp home system, so defaults to that if MAF fails or is disconnected.  Makes diagnosis harder than if it just would no longer run.  I read lot of posts where people having hot idle problems replaced the MAF, and in none of the cases did it solve the problem.  Usually the IAC didnt either.  Some got relief replacing the TPS.  Some found a vacuum leak.  xcUsually they just seemed to live with the problem.

Prior to this Ranger, only computer fuel injection I have owned was an 80s TBI Cavalier which actually was pretty reliable,  and a 91 TBI Olds Calais which I never drove, just bought with a bad head, fixed, and resold.  So I am not very fluent in computerized cars.

Having grown up with non-computer carburetor vehicles, I still dont get the need for complex computer stuff.  When properly tuned and car geared for economy,  a carb engine can get nearly same fuel mileage.  However what carb engine cant do is get both fuel mileage and meet arbitrary emissions standards.  Frankly IMHO, if a carb engine can get good fuel mileage, it isnt polluting anymore than a computer engine getting same mileage.  What was stupid was back in 70s putting on bunch gizmos and detuning engine  to meet percentage limits on certain pollutants, but fuel mileage went south big time.   Such nonsense gave carbs a bad rep.  I had a '71 Buick LaSabre (heavy car, pre-pollution controls) with the Buick 350 V8, TH350 transmission, point ignition, 2BBL carb.  On long trip, it got an honest 22mpg, 13mpg in town.  (Yea the Buick 350 did much better than most V8s on fuel mileage, it was long stroke, most that size, like Chevy 350, were short stroke) Now I drove a '79 Buick, same engine EPA'd to meet '79 pollution standards.  It got 13mpg hiway, 9mpg city.  Are we really saying a car getting 13mpg pollutes less than one getting 22mpg?  Really?

[Deleted]

Sounds like a IAC. Spend the extra $ and buy a motorcraft part. I had bad luck with aftermarket IAC's, and electrical parts are non-returnable, so I'm out $80 for a cheap IAC

[hermitjohn]

Ok, so I take it, the IAC is supposed to stay moved (open?) for more than couple seconds? Isnt having it open just suppose to add bit air and raise idle speed when engine cold? Isnt it supposed to be closed when engine hot? The problem is too low of an idle speed with engine hot. Is IAC supposed to open at any time necessary to keep idle speed constant, hot or cold engine?

Like say, I didnt run across anybody in Ranger forums with hot idle stalling problem curing it with new IAC though that seemed one of first things everybody tried.

Thats the trouble with the modern stuff, just cause something would at first blush seem like logical answer, it isnt necessarily the answer. Every dang thing is sort of interconnected, codes thrown up can be from secondary things triggered by the primary problem. So you end up throwing money and parts at it, in a sort of whack a mole game. Said before best thing on modern vehicles is to own a second identical vehicle, so you can just swap out parts to hearts content until you discover the right one, then buy that one.

I suppose I should take it to Autozone and get them to do a read out the codes, though I imagine with mileage it has, its got plenty. And maybe nothing to do with the actual problem.

Its ok engine and right size, but not wanting to put much money into it, as I think I will be swapping in something else just so I can have a granny four speed transmission for my hill. Ford in all their wisdom just offered light duty transmissions in Rangers. Fine for a four cylinder but not for a 4.0L. They should have used next heavier duty Mazda 5spd with the 4.0L that they used in their F150. Not that it was what one would call heavy duty, more like "light duty plus". But it could hold up to that size engine if not abused.

[hermitjohn]

Hmm, what about a faulty EGR, guess they still used that in 90s? Anyway if its not closing properly at idle, that could cause engine to stall. Least it would cause low rough idle back in day when it was a vacuum operated valve on pre computer cars. Course back then you could just block it off and probably even get better mileage. Sure that isnt the case with computer car. No doubt the computer has a fit if it isnt working properly.

[hermitjohn]

Common Symptoms of a BAD EGR Valve

The following are the most common symptoms that a Ford (or Mercury or Lincoln) car or truck will usually experience when there's a fault in the EGR System:

Car or truck runs fine, but the check engine light (CEL) is on with an EGR Valve Fault Code:
P0401 EGR System Flow Insufficient.
P01406 EGR Valve Pintle Position.
Rough Idle.
Really BAD gas mileage.
Lack of power as you accelerate the vehicle down the road.
Car (or truck or mini-van) seems to run ok above 30 miles and hour but once you come to an idle, the engine barely stays running and/or idles rough. Once you take off again, it runs OK.

[hermitjohn]

A common EGR problem with many Fords is a bad DPFE (differential pressure) sensor. The DPFE sensor is part of the EGR system and senses EGR flow when the EGR valve is open. It provides a feedback signal to the engine computer so it can vary EGR flow to meet changing engine loads. The DPFE sensor is usually mounted on the engine and is connected to the pipe that runs from the exhaust manifold to the EGR valve with two rubber hoses. When the sensor goes bad, the Check Engine light comes on and typically sets any or all of teh following fault codes: P0171 & P0174 (lean codes), and/or P0401 (insufficient EGR flow). Nine out of ten times, the fault is not a bad EGR valve or a vacuum leak, but a bad DPFE sensor. A replacement costs about $112 at Ford, or about $48 at an aftermarket auto parts store.

[Deleted]

I don't think a basic scan tool/code reader will work for a IAC issue. The IAC is receiving voltage, so it fakes the computer out. When the car stalls out, it will throw a code for MAF or some other code because that's what the computer sees first.

I bought a 02 focus last summer at auction. The car was listed as starts and dies. When I got the car on the hoist, you could see the PO was throwing parts at it, in hopes of finding the issue. It was crazy parts like new timing belt, Fuel filter, after market air cleaner, MAF and other parts.
I used a Snap-On modis to find the issue. We split the screen into 4 graphs so we could monitor 4 items at once.
With out monitoring the sensors to see where they were at, a handheld code reader would have done me no good. 

[hermitjohn]

Ok, my engine starts and runs fine when cold. Doesnt try to die at cold idle. If anything, it seems bit too high, around 1500rpm, fast idle on a OHV engine should be around 1000rpm, hot idle around 600rpm. It seems to have enough power. 16mpg sucks but its not super bad fuel mileage for this engine. Cologne engines just never were mileage champs in any incarnation. Its only at hot idle that it wants to get super low rpm and die. Along with the crunchy gearbox that pops out of first gear, makes driving through a box store parking lot, a whole bunch fun.

so my question again, is the IAC only a cold engine "fast idle" control for computer fuel injection, or does it function at all times to constantly adjust idle? I ran across this sort thing on 70s VW and Volvo with non-computer Bosch fuel injection. They called it something like auxilary air valve. It was just to give fast idle on a cold engine so it wouldnt die. So as engine warmed up, it closed.

I already discovered that the MAF is not a real factor, truck runs ok without it, cold or hot. Replacing belt or whatever is just silly unless perhaps your previous owner noticed it needed replacing, not to cure stalling problem, just cause it was brittle/cracked. Sometimes you discover potential problems unrelated when searching.

The EGR or the sensor that monitors it makes sense if it is off cold but not properly shutting down at hot idle. EGR should be off below 30mph hot or cold.

Be nice if I could actually find the EGR or the sensor. The Haynes manual is about as useful as a roll of Charmin. It shows pics of a "typical egr" on a four cylinder. Whoopeee. Seems the 3.0L doesnt have an EGR. The 4.0L has one but only clue is that its on rear right side of intake manifold. If its there, its under the coil pack. cold and getting dark when I looked last evening so didnt try to take anything apart to find it. RockAuto.com did show me what both the Ranger EGR and sensor look like. Though oddly they only show the sensor being for California version of 1994 Ranger. The EGR valve itself is for all 4.0L. So suppose its possible the 49 state version EGR was just vacuum controlled like in pre computer days???

I figure it isnt going to hurt anything to unplug the vacuum line to EGR valve and plug the line. See how the engine acts when warmed up. EGR simply shouldnt ever open with vacuum line disconnected. At worst it should cause knock/ping out on hiway, but should have polite manners at hot idle unless computer tries to fight me. There is some complicated procedure to use a vacuum pump to test it, but come on... I only go digging for vacuum pump I havent used in years if there is no other way.

[hermitjohn]

Ok, I found pics of EGR valve and DPFE sensor on an OHV 4.0L, front right of the engine of course, Haynes naturally useless in its description, but pics I found were for like 1997 and up. Shows DPFE just below IAC and the EGR below that hooked to drivers side exhaust manifold with a tube. Not there on mine. Little more research shows Federal 4.0L engines didnt have EGR in 1993, only had EGR with California emissions. Mine is 1994, so maybe my truck made in 1993 for 1994 model year and somehow legally got produced without an EGR. Or perhaps somebody just swapped a low mile 1993 engine into my truck. I mean the engine seems very clean and good power for one with close to 200k miles shown on odometer. Actually the whole truck seemed a little too clean, with exception of the transmission. It was dirty filthy thing that looked like it was off a high mile vehicle out of a pick-a-part junkyard. Probably was as it was 2wd transmission and the truck came from factory as a 4wd.

I looked closely at both exhaust manifolds and no tubes from an egr. There is a boss in drivers manifold casting where in future years there would be a threaded hole for egr tube.

So kinda back to either TPS or IAC. Now what happens if I remove the IAC, weld up a plate with two ports matching the holes. Then use an old style all metal heater control valve manipulated with choke cable to control air bleed between the two ports, and thus idle speed? Does computer freak out that its signals sent to IAC does nothing?

Course if IAC is just cold engine fast idle control, then it should be closed at hot idle. Meaning most likely problem is the TPS. Any air leak would mean faster idle so not an air leak. When hot this engine idles down to like 300rpm and usually will stall out soon after if I am not feathering the throttle.

[hermitjohn]

Ok, going to try and clean the IAC. If that doesnt work and I have to gamble, betting on TPS, besides that, can get one for $20. The IAC is not cheap. If TPS doesnt solve it, will rig home brew air bleed to control idle with choke cable. Leave IAC doing its thing.  Just add an auxillary air bleed controlled with heater valve and choke cable to up the hot idle.

[Deleted]

Clean the TB and MAF with throttle body cleaner, slightly different than standard carb cleaner. TB cleaner eats crud better IMO. The TPS should have a slight adjustment on it, mark the location, and try to tweak it. Make sure the air box has no air leaks. Also, make sure the thermostat is working. If the computer see's a engine that is cold, it will also try to tweak fuel trim & etc. 

All the computer management items work together, i.e. if the MAF is not in parameters, it tells the computer to tweak a different sensor to make the engine perform.
Just like a O2 sensor helps control fuel trim.

[hermitjohn]

If computer sees engine as cold, isnt it going to try to keep a high idle speed rather than try for an unusually low idle speed? Anyway, dash temp gauge shows engine into operating temp range quick enough that I imagine the thermostat is ok.

Yes, really annoying to have computer try to out think me and compensate for any changes I make. However if necessary, believe computer will not be able to compensate for an extra intake air bleed that I create and control manually. No more than it can compensate for an unplanned uncontrolled manifold leak. Somebody on one of forums mentioned they had a high hot idle speed on one of these engines. Couldnt find a leak, said it turned out to be a lower intake manifold gasket leaking underneath a valve cover. Now thats a hard one to find.

[Deleted]

IAC is know for idle problems on Ford. Mine had no rhyme or reason...would idle fine...then can't keep it running at stoplight...would not idle cold..etc. Thorough cleaning and purrs. Used an entire can of carb cleaner to get all the gunk out of it.

[hermitjohn]

Nobody has answered my question whether the IAC is mostly to increase cold idle speed, or if it also partially opens, just lesser amount, to keep idle up when engine hot???? That fully closed, idle would be too low. I suppose that depends if the throttle valve completely closes and this controls idle completely, or if its just an auxillary air bleed for cold engine idle. I can see engineer using it either way, depends how close a control they wanted on engine idle speed for emissions reasons.

Its not a big deal to clean stuff and do cheap experiments to get hot idle up so it doesnt stall. But since I am most likely going to have to replace this engine with an older carb engine in order to have a granny four speed to replace this worn out light duty transmission, then I dont want to put much money into current setup. I need a granny gear to deal with my hill so I am not having to do running starts. Running start to go up steep hill, is hard on any vehicle. The truck handles well and comfortable to drive, other than the hot idle stall and the noisy transmission popping out of first. Figure any 6cyl this size isnt really going to do much better than 20mpg in this weight vehicle, unless I make it painful to drive with super tall rear axle gearing. Even small V8 probably about same. I am just not fan of V6 engines, though from experience I know shoehorning a straight six into a Ranger is time consuming. And if I am putting energy into all that, can pull the six in my old Ranger to fix its oil pan and have 4wd small pickup again. Its just not as comfortable to drive as this newer Ranger. Old Ranger feels pretty cramped compared to this one.

[Deleted]

Don't have exact answer to your question. I did some research and decided to start with cleaning IAC as it was going to be about 3 bucks for a can of carb cleaner. Since it was motorcraft I believe it is original..30 years old. I separated mechanical and electric part then cleaned it thoroughly...no problems since.

[hermitjohn]

Well thats definitely place to start, doesnt get much cheaper than can carb cleaner. Though more I think of it, wouldnt surprise me if it is a bad TPS.

I've never heard of TB cleaner other poster mentioned, but I will keep eye out for it. If as he says, its a more potent carb cleaner then its useful to know about. And of course could soak the non electric part in seafoam, that stuff is suppose to be pretty effective to de-carbon parts.

[Deleted]

I spent about 15 minutes taking off...cleaning..back on. I was ready to replace all the sensors...but that's pricy. As for the 4.0...I have had three explorers with the 4.0 and have my eye out for another one...very reliable and plenty of power...never had engine troubles with any of them. Not the best mileage but ok for explorer. 300,000 and running well is common...tranny will go first.

[hermitjohn]

I took IAC off and then removed step motor from it. It wasnt that dirty, but I sprayed it. The plunger part of it seems to work fine, closed it cut off auxilary air, open it let it through. but I suppose step motor could be dodgy. Said Ford on casting.

Think though its likely to be the TPS. No cleaning that, it either works properly or it doesnt. Going to order cheapest new one I can find, little less than $20, see if it makes a difference. I dont live near a pick-a-part salvage or would buy used one. See if the used one changed anything. I assume they sell them for like $5. any more than that, you just well buy cheap new one. Guessing might be worth keeping a spare in glove box, especially if one buys a cheapie.

[hermitjohn]

Ok, its that dang damp cold outside that cuts through you.

But I went out and played with Ranger. I changed my mind, think now it is IAC. Reinstalled it after cleaning. Cold fast idle was 1100. Thats about right. But after few minutes, it went up to 1500??? Then I unplugged wires from it. Default unplugged setting is for it to be completely closed. Super low stumbling idle like it was doing to me in parking lot with engine hot. Enough air must get by the throttle valve or through the IAC for this low stumbling idle.

And it is just an automated air bleed. But the air let in by the IAC has to be air metered by MAF and diverted before the throttle valve. Cant just open an outside leak into manifold or the fuel mixture in cylinders will be too lean. The computer adjusts fuel by amount of air going to engine as measured by the MAF. Whether that air, once it passes the MAF, goes through throttle valve or the IAC doesnt matter. Same total amount air being used by engine, same total amount fuel being given to the engine.

So as long as I manually control the air flow through same route the IAC draws its air, the computer still happy. And I can set it to cold fast idle at 1000 and to hot slow idle at like 700 via a choke cable run inside to the dash and using a cable controlled heater valve to control amount air and thus idle speed.

Now I also discovered that the IAC is supposed to bump up speed when big power draw like air conditioner is turned on, which otherwise will normally slow idle. Like on older carb cars, one just picks a compromise hot idle speed that isnt slow enough that load like turning on air conditioner slows engine enough to stall it. Yet the hot idle isnt racing the engine. I know in 70s they even developed vacuum controlled gadgets to up the idle speed if you turned on air conditioner. Guess I never owned a 70s car with a working air conditioner as I never had to tinker with such. Jalopies I owned, was happy if they ran and the water pump and alternator worked and they moved down road at half way reasonable speed. Extra luxury options werent a priority.

I even found an old heater valve, so I get some warm weather to actually want to work outside, can play with making an adapter plate to connect hoses for the heater valve to control idle. That will once and for all confirm what I wrote above. Or confirm that I am just full of beans and feeling musical...

And hey there is a cheap TPS on its way. Can swap that out, though at this point, probably wont make lot difference. But doesnt hurt to have spare in glove box in plastic bag. Suppose really ought to snag a MAF at some junkyard to keep in glovebox too though it should run in limp home mode if MAF fails.

I did research new IAC. As another poster in this thread said, you really want a genuine Motorcraft IAC. Thats consensus of people posting about Fords of various models and years that use an IAC. Cheap generic ones tend to have not so great stepper motor and thus dont control well and dont last. But I like this idea to manually control the idle air bleed and thats what I am going to do. If that becomes tiresome, can always buy a MOtorcraft IAC and go automagic again.

[Deleted]

Jan 20, 2016 22:49:54 GMT hermitjohn said:

Ok, its that dang damp cold outside that cuts through you.

But I went out and played with Ranger. I changed my mind, think now it is IAC. Reinstalled it after cleaning. Cold fast idle was 1100. Thats about right. But after few minutes, it went up to 1500??? Then I unplugged wires from it. Default unplugged setting is for it to be completely closed. Super low stumbling idle like it was doing to me in parking lot with engine hot. Enough air must get by the throttle valve or through the IAC for this low stumbling idle.

And it is just an automated air bleed. But the air let in by the IAC has to be air metered by MAF and diverted before the throttle valve. Cant just open an outside leak into manifold or the fuel mixture in cylinders will be too lean. The computer adjusts fuel by amount of air going to engine as measured by the MAF. Whether that air, once it passes the MAF, goes through throttle valve or the IAC doesnt matter. Same total amount air being used by engine, same total amount fuel being given to the engine.

So as long as I manually control the air flow through same route the IAC draws its air, the computer still happy. And I can set it to cold fast idle at 1000 and to hot slow idle at like 700 via a choke cable run inside to the dash and using a cable controlled heater valve to control amount air and thus idle speed.

Now I also discovered that the IAC is supposed to bump up speed when big power draw like air conditioner is turned on, which otherwise will normally slow idle. Like on older carb cars, one just picks a compromise hot idle speed that isnt slow enough that load like turning on air conditioner slows engine enough to stall it. Yet the hot idle isnt racing the engine. I know in 70s they even developed vacuum controlled gadgets to up the idle speed if you turned on air conditioner. Guess I never owned a 70s car with a working air conditioner as I never had to tinker with such. Jalopies I owned, was happy if they ran and the water pump and alternator worked and they moved down road at half way reasonable speed. Extra luxury options werent a priority.

I even found an old heater valve, so I get some warm weather to actually want to work outside, can play with making an adapter plate to connect hoses for the heater valve to control idle. That will once and for all confirm what I wrote above. Or confirm that I am just full of beans and feeling musical...

And hey there is a cheap TPS on its way. Can swap that out, though at this point, probably wont make lot difference. But doesnt hurt to have spare in glove box in plastic bag. Suppose really ought to snag a MAF at some junkyard to keep in glovebox too though it should run in limp home mode if MAF fails.

I did research new IAC. As another poster in this thread said, you really want a genuine Motorcraft IAC. Thats consensus of people posting about Fords of various models and years that use an IAC. Cheap generic ones tend to have not so great stepper motor and thus dont control well and dont last. But I like this idea to manually control the idle air bleed and thats what I am going to do. If that becomes tiresome, can always buy a MOtorcraft IAC and go automagic again.

Maybe more cleaning...seems 1100 high idle and about 600 normal is where I am. Yes it does kick up a notch when ac is on. Motorcraft...or other top brand because...I am on the third set of all four inner and outer tie rods...second steering box...second master cylinder and brake booster..u joints..ignition switch..caliper bushings are shot causing pads to wear uneven...all lifetime warranty house brand's from three big name parts stores. Never again. That is in 35k miles. In the spring I will tear entire front axle apart...all Spicer..Dana..Motorcraft parts.

[hermitjohn]

The little plunger in the IAC is putting up no resistance, clean as its going to get (wasnt that dirty to begin with) gotta be the stepper motor, or I suppose computer controlling the stepper motor or of course wiring between them. From what I read, when IAC needs cleaning, usually there is lot carbon build up so plunger thingie is very limited in its ability to move. One on mine puts up no resistance moving it with my finger with stepper motor removed, has good range of motion. So its just not being moved properly by the stepper motor.

The front end on this truck is amazingly tight for the miles on it. I was pleasantly surprised, usually high mile vehicle means one has to go through front end and replace lot stuff to get it tightened up so it doesnt wander all over the place going down the road. Does need new dust/grease boots on the various tie rod ends and such. Some cracking and small tears. You catch them early and the joints just dont have chance to go bad. Worn joints with bad boots means somebody wasnt paying attention. Have yet to see a bad joint with an intact boot. The aftermarket polyurethane boots arent much more expensive than the replacement rubber ones, and last literally forever. The rubber replacement boots are junk. The boots on cheap replacement tie rod ends and ball joints, unlike OEM, seem to self destruct very quickly too. Soon as boot fails, if not immediately replaced, you start joint wear as water and grit get inside.

Steering boxes just start leaking. Not sure if one can buy the seals to rebuild them yourself when leaking starts or not. Moog steering parts nice when you can get them. But like I say, you put the polyurethane boots on any greasable joints and actually grease them regularly with a heavy grease, and they last ok. Not sure why modern chassis grease available in parts stores is all the thin stuff that dissipates quickly. But you can track down better stuff. Anymore have to buy it online, the auto parts stores people are clueless and all the tubes/cans are sealed so you have to buy the stuff to find out whats in it. So called "heavy duty" written in large letters on can means nothing. You have to get the microscope out and read thickness rating and hopefully what they used to thicken it. Adding garbage to thicken it does not make good grease.

[comfortablynumb]

Willows old ranger was doing a similar thing...

Careful cleaning that IAC unit if you get cleaner in the wrong place it messes it up.

Clean the MAF with MAF cleaner. Clean it a lot. Twice. It caused a lot of issues. Also in the air intake tube from the MAF to the throttle body ther eis aair temp sensor.... clean that with MAF cleaner too. That thing as small as it is reports the intake air temp to the computer and adjusts the fuel mix. When its dirty, the mix is all off.

Clean the throttle body out very well. use a toothbrush and a rag and lots of cleaner. Carbon build up in there will interfere with the plate opening and closing, and that in turn directly messes with the TPS.

I have willows old truck engine all apart putting a lower intake gasket set in.... so I removed the fuel injectors and the fuel rail to clean them and replace o rings and gaskets. You problem could very well be old O rings sucking air, or making a loss of compression. Your fuel rail gasket or upper intake gaskets could be sucking air also. Even a small leak here or there can cause rough idle after warm up. When I I removed them on this one here, the lower intake bolts were almost finger tight.... not good. so were the upper intake bolts and also the injector O rings were hard and the injectors almost fell out. I think all these leaks were contributing to the idle problems it was having.

But the gasket blew out on the water port so... everything is getting replaced and cleaned.

The rough idle issues pretty much went away the 3rd time I flushed out the MAF. But I did replace the plugs wires and coil pack too... so who can really say what did it.

And this one is a 2000 so it has an OBD2 computer I can plug in and track the live data. A 94 doesn't so yours is a tough nut. YOu'll need a code scanner that fits those pre OBD2 computers.

From what you describe... I bet you have a leaky intake somewhere.

[comfortablynumb]

Question:
Is there any running conditions when it runs normally?

[hermitjohn]

When I removed the MAF, buisiness end with the two little wires was clean as a whistle. There was NOTHING to clean. NOT ONE SPECK of carbon. Assume previous owner must been throwing new parts at it. Seems to be what desperate people do on computer vehicles. You can put on all new sensors and still cheaper than taking it to a mechanic that may or may not know what he is doing.

Its just the idle, little too high when cold, low and stumbly with engine hot. Not a leak cause it wouldnt be super low at hot idle. Small manifold air leaks cause high idle hot or cold, unless huge leak, then engine wont idle at all as idle mixture is too lean. For instance on a vehicle where vacuum hose to brake booster comes off or cracks. And was weird that it started out 1100 at cold idle when I first started it, THEN went UP to 1500 after few minutes before engine fully warmed. Should be on its way down as engine warms. Pulling the electric connection closes IAC completely, and gave same low rpm stumbly idle that I get at town in parking lots. So I am assuming IAC is basically going from open to closed as engine warms up, its not properly adjusting gap in increments to actually regulate idle speed properly. That would be the stepper motor causing that, not the plunger area. And I removed the stepper motor to clean plunger area, dont want carb cleaner in an electric motor.

I suppose there is some instant in there on warmup where idle is perfect. But if engine is warmed up fully, you get the low stumbling idle.

Anyway this isnt time critical so I can putter and experiment. I only drive it to town twice a month, and truck is drivable, just annoying in town feathering the gas while holding it in first gear. No problems at all once one gets much above idle.  Hey I have had lot experience with carb engines.  Every one had their prefered hot idle speed.  Set it too low, even if it was still smooth and it would stumble a bit on take off.  Same thing with Ranger, hot idle is just too low so even feathering it you get bit stumble initially going up to speed.

I use the 4wd F250 to drive down the county road to the USPS clusterbox. So much easier to use 4wd getting up my really steep driveway, though the Ranger has lot less problem than the Festiva did. Much bigger tires and lot ground clearance. It can take the abuse much better than Festiva. Someday my neighbor owning property along my access road promises to go in with me on hiring dozer guy. Yea, and someday pigs may fly... I've hired it fixed before. Its expensive and only lasts two or three years. Not worth it where I dont have to get in and out daily. Or if you hire cheap guy with little dozer that doesnt do it properly then it might last less than a year.

[hermitjohn]

Oh, interesting tidbit I didnt mention. I have been leaving Ranger with negative battery cable disconnected when setting so it wont drain battery.

Well this apparently resets the computer. Noticed during my experiment after cleaning IAC, at first no check engine light, then when idle went from 1100 to 1500, check engine light lit up. So indeed might be worth having the Autozone boy retrieve code next time I am in town. Probably useless info, but might be useful.

Could be computer is trying to compensate for something raising cold idle rpm?? Still doesnt explain the super low hot idle speed. That is pretty much going to be an IAC that completely closed instead of adjusting properly.

[hermitjohn]

Whee, got a $17.61 lesson in cheap TPS. And what a truly faulty TPS can do. I had ordered it and got it today, so went ahead and put it on Ranger, started it up. Check engine immediately lit up. Idle speed up and down, stalled twice, finally settled in at 700rpm. I then press gas pedal and it stumbles around with no power, and wont go over 2000rpm.

I shut off truck and put old one back on. Same as before, cold idle at 1500, but it has plenty power, no hesitation.

Looks like one needs to buy all Motorcraft brand sensors unless one wants to just toss money.

But also tells me it well could be the TPS. Such an amazing difference in the engines "personality". Just if I am going to buy one, get quality one.

[Deleted]

Jan 21, 2016 18:34:03 GMT hermitjohn said:

Oh, interesting tidbit I didnt mention. I have been leaving Ranger with negative battery cable disconnected when setting so it wont drain battery.

Well this apparently resets the computer. Noticed during my experiment after cleaning IAC, at first no check engine light, then when idle went from 1100 to 1500, check engine light lit up. So indeed might be worth having the Autozone boy retrieve code next time I am in town. Probably useless info, but might be useful.

Could be computer is trying to compensate for something raising cold idle rpm?? Still doesnt explain the super low hot idle speed. That is pretty much going to be an IAC that completely closed instead of adjusting properly.

Could be...when battery is disconnected the powertrain control module loses it's memory and abnormal driving symptoms may result for ten miles or so until the pcm relearns its adaptive strategy. That is for an 1986 with EEC. Yours may be the same.

[comfortablynumb]

If thats an adjustable tps it has to be very carefully set/tested with a multimeter.

www.therangerstation.com/Magazine/winter2009/throttle_position_sensor.htm

But it does sound like the AIC valve is sticking.

If it pops the CEL on... get the code. Whatever is tripping the code is probably the problem.

You can do it yourself
www.therangerstation.com/tech_library/OBD_I.shtml

I had a 92 that I just bought a 12 buck scanner for... much easier. It came in handy several times.

[hermitjohn]

Nope, TPS not adjustable on my Ranger. Only goes on one way with no adjustment. Have seen those with the slots that have little adjustment available, but think that was on 80s era cars. EPA doesnt want anything adjustable or user friendly from the factory.

If IAC is sticking, its the stepper motor, the plunger part of it is definitely not sticking.

May sound like dumb question, but where is the self test connector? They tell you how to connect things to it on that link, but not where it is located.

[Deleted]

Should be on the firewall under the hood...never used mine. Sound like an ordeal to troubleshoot according to my shop manual.