I know this is beating a dead horse. I've read and read and read about it, but can't seem to get my questions answered. So here's the skinny.

I recently purchased a used 90 model XJ. It has the usual 4.0/auto. It hard to start and usually requires a little assistance from some starting fluid at first. Once it fires it will run just fine, except the idle is out the roof. I have cleaned the throttle body, and replaced the IAC. The problem lies where the IAC port is on the throttle body. Something is or isn't telling the IAC to go far enough out to stop the air from coming through the hole the pintle is supposed to be in. I took an old IAC that I had laying around and broke it so I could manually set the pintle. With the idle set manually this way, I unplugged the one I had broken and plugged the new one in just to verify that it was working correctly. It is working but it will not go all the way out to where it should be. If you turn the key off, the IAC will reset by spinning itself back to a certain point. So I have no doubt that it's not working. I did replace the ECM just for giggles to make sure and eliminate that part of the equation. Is there anything that could cause this? Or are there any suggestions you guys might have that could remedy my problem?

 

vacuum leaks will also cause high idle and is the gasket/o ring on the iac

 

Yes the o-ring is on the new IAC. Also, the vacuum leak is the problem. Its the IAC port that is leaking as the pintle isn't closing the port off like it should creating a HUGE vacuum leak. This is looking up through the bottom of the throttle body after I cleaned it. The pintle is where it reset to as soon as I turned the key off.

 

You have no idea of how the idle circuit works, do you? The IAC controls the idle speed as the name implies, that is not a vacuum leak that you are hearing at the IAC port inside the throttle body, that is air being sucked in so the engine can idle. But if there is a vacuum leak coming from someplace on the intake or any of the hoses and lines it will throw the IAC motor position out of wack because it is trying to correct the idle speed. If you have a huge leak the IAC will close almost completely.

 

Yes, I do know how it works. The motor is sealed up. No vacuum leaks. I have tracked down all my lines and double checked them. Also checked the intake/exhaust manifold bolts and gasket. I wasn't calling the IAC port a vacuum leak. Just comparing it to that. Sorry if my wording was misconstrued. Essentially its just pulling air by it, and speeding up the motor. It's not that complicated. You can take your finger and put it over the port and the idle drops to where it should, (simulating the closing of the port). But you said that if you have a huge leak the IAC will close completely right? Then if the motor is sealed up, is that why it's almost 3/4 of an inch from closing off the hole like in the pics? Still the idle is like 3000 rpm, because the IAC isn't closing at all. Something is not telling it to close off like it should. I simply can't find it.

 

Forgive my a-holesness, didn't have my coffee at the time I posted. Do you have access to a scan tool (not a code reader)? Do a functions test on the IAC with a scan tool and see if it responds. There may be a damaged wire in that circuit, but if nothing like that checks out I coudn't tell you what the problem is without having the Jeep in front of me.

 

do all the temp sensors work properly? if for some reason it thinks its cold it may cause a high idle

 

are all the sensors working properly? tps?

 

Bustedback- No worries man. Thanks for the reply, but no I don't have a scan tool. I was looking into the TPS maybe. If the system is thinking that the throttle body is "too closed" perhaps, it might be trying to open the IAC more. I found a page that tell you how to test a TPS on this model. That is going to be what I try next. Just hope it's something simple that I don't have to throw a bunch of parts at.

 

Did you set the IAC to the correct length before installing it?And if you did set it did you measure the length from the correct spot?
It is possible that you purchased a broken IAC motor.I would try a different one before getting into the other stuff.

 

The instructions in the IAC did say that if it was TOO LONG to set it. Not if it was too short. And it needed to be less than 1 1/8th of an inch. No more or damage could occur. I really didn't want to break it since it was 65 bucks. Those little boogers ain't cheap. But I thought about that too. The downside is the one I pulled off wasn't working correctly either, so measuring it wouldn't have done any good.

Also, the IAC motor IS working. It's just not out to where it should be. I had it out and could feel it moving trying to adjust, and then when the key was turned off it spun back to reset to help with the start next time. It just is nowhere near the place it should be.

 

I've replaced hundreds of IAC motors over the years at Dodge dealerships and in fleet service jobs I've had. I've never had a problem the the engine idling too high after it goes through the relearn when replacing the IAC motor. I start the engine and put it in gear and let it idle for a few minutes with the A/C off. I never pulled the pintle out or pushed it in when installing, just put it in and started the engine.

 

exactly plug and play

 

The adjustment was just a suggestion based on my experience with other vehicles I have had and the instructions that came with the IAC for those vehicles.I have not replaced an IAC in a jeep So my suggestion could have been wrong.Was just throwing the idea out there.
The IAC for my s-10 came extended and you had to rock it in slowly with your thumb until it was at the correct length.It was also mentioned in the instructions that you should not adjust a used IAC with this method or you could break the IAC.

 

Thanks for all the suggestions. Still trying to diagnose it. When I find a solution I'll post it up. Thanks again