IAC woes ... at least I believe it's IAC

[BLHTAZ]

I replaced the IAC back in January because I was having some very intermittent idle issues. Things seemd fine until a few weeks ago and the idle issues started again and have become progressively worse.

 

When the truck is started...it will rev up to as high as 3500 RPM and will sometimes stay there for as much as a minute if I allow it to and other times it will calm down to normal (650 - 700) in just a few seconds. Usually I have to shut it off and start it again a few times before I can get it to slow down and if I start driving with it at high idle, it typically has no effect.

 

I took the big air intake duct off of it today and started it up. It immediately went to 2500 and stayed there until I put my finger over the IAC hole on top of the throttle body and it slowed down to normal idle so I know that the IAC is staying open when it shouldn't.

 

Is there another way to test the IAC itself other than with the testing tool that is described in the FSM? I have ordered another IAC for Monday, but I am only "ASSuming" that it is the problem right now and hoping that it's not the ECU.

 

I put a new TPS on it too just for the hell of it, but that made no difference at all so I now have a brand new TPS to sell if anyone needs one ;)

 

Within the last year these items have been replaced...

 

IAC

TPS

o2 sensor

MAP sensor

 

Could the CTS (Coolant Temp Sensor in the block) be an issue here?

[ejndssn]

what about the egr valve have you replace that as well :hmm:

[rworks]

I would remove the IAC again and clean the piss out of it. Also remove the throttle body and clean the hole where the IAC sits.

 

I used Gunscrubber to clean the throttle body, but brake cleaner would work too.

[BLHTAZ]

I have not replaced the EGR valve, but that was on my mind. It just didn't seem that it would be a root cause for this issue as it doesn't seem to matter if the engine is hot or cold...it just wants to run at 2500 - 3000.

 

I have taken everything apart and cleaned it thoroughly today, but it made no difference.

[comancheman]

mine just recently started doing the same thing. i was leaning to iac also. it seems worse when its damp out. i don't know why this would be though

[FxRacing282]

I have not replaced the EGR valve, but that was on my mind. It just didn't seem that it would be a root cause for this issue as it doesn't seem to matter if the engine is hot or cold...it just wants to run at 2500 - 3000.

 

I have taken everything apart and cleaned it thoroughly today, but it made no difference.

 

push on the bottom of the egr when its running. if it moves its good.

 

and 2X on the throttle body clean. the IAC has its own "port" and it gets clogged with carbon buildup and so you have to clean it. if you use too much of anything to clean the IAC port pull plugs and crank. don't let it drain in the crank. we use break away and a toothbrush at work.

[Pete M]

If the throttle body is to remain on the vehicle during cleaning, use an o2-sensor-safe throttle body cleaner to clean it. The old carb cleaners can hurt the o2 sensor.

[BLHTAZ]

I have taken everything apart and cleaned it thoroughly today, but it made no difference.

 

Cleaning has been done as I said above... ;)

 

It appears that there is no way to truly test the IAC without the proper tool for doing so, so I have ordered another one to replace it again. We'll see what happens. I think I am going to replace the EGR Valve as well...just because :brows: . I'm sure it couldn't hurt after 21 years.

[BLHTAZ]

The new IAC is in and it is running perfectly :D

[Oizarod115]

i figured it would be the IAC, i unplugged mine a few days ago playin around and it idled up to 2500-3000 v

 

vacuum leaks tend to not be intermittent and don't usually change when you turn it off/on

[eacomanche88]

Just a question Brent, Does the shop your at still have a DRB I? It's the real small one that pre 90 Jeeps will work on. There is a actuation test you can do to check the IAC. you can raise and lower the idle with the scanner. If the idle does not change, stuck IAC. I Have worked in Chrysler/ Jeep dealers since 1987. Had to shake the cobwebs out on this one.

 

P.S. My 88 does the same exact thing.

[BLHTAZ]

Just a question Brent, Does the shop your at still have a DRB I? It's the real small one that pre 90 Jeeps will work on. There is a actuation test you can do to check the IAC. you can raise and lower the idle with the scanner. If the idle does not change, stuck IAC. I Have worked in Chrysler/ Jeep dealers since 1987. Had to shake the cobwebs out on this one.

 

P.S. My 88 does the same exact thing.

I know of that tool, but I don't know if anyone has one at the dealership. I was going to start asking around, but I just took the chance and replaced it as it really seemed to me that it couldn't be anything else but the ECU and that is not likely as they rarely ever go bad.