ibmike150

I threw a code for a bad idle air control system so I put a new valve in and now I get a super high idle, from 1500 to 2800 if i tap the gas. I'm throwing a code for bad battery temp sensor (charging system bypasses anyways) and tranny range sensor. Not sure what could be causing such a strange idle.

zjguy

check vacuum lines

macgyver35

I usually go back to what I last touched, if it was recent, when something goes wrong.

Three things come to mind:

1) Did you adjust the IAC correctly? When I replaced the one in my 02 TJ, I had a hell of a time with high idle for a bit, until I realized I adjusted it wrong and had to re-do it.

2) Are you sure you have the O-ring seal on the IAC correctly. It could have gotten pinched or torn, which will cause a leak below the throttle plate, resulting in high idle..

3) Did you remove the throttle body to change out the IAC? If so, are you sure there was no damage to the throttle body gasket, and that you got it back on square and flush with the bolts properly tightened? Any of this could also cause a below throttle plate leak resulting in high idle.

All of these things can happen easily, and are also easily missed during reassembly.

Take some WD-40 and spray around the base of the throttle body and the area where the IAC mounts and see if you get a momentary change in idle speed. This will be a sign of one of the conditions I mentioned above.

ibmike150

i ran the engine with the air intake hose off and air was rushing into the idle bypass and when i put my finger over it to cover the hole it dropped in idle, could be bad valve? how do you adjust the valve?

OleBlue

You cant adjust the IAC on an xj.

It is likely that your old iac was bad and the computer was compensating for it. Now you have a new one on, did you reset the computer?

macgyver35

Not necessarily true. It depends on the brand of IAC you get. I believe the one I bought was a NAPA brand, and the instructions that came with it indicated 2 or 3 initial adjustments that had to be made to the "needle" depending on your vehicle. You rotated the needle to get it to an initial projection distance. It was threaded. Once you had it measured as projecting the right distance you locked it in, then you installed it. I missed that during the initial installation, and had crazy high idle at first. Went back and followed the instructions and the idle settled out the second time correctly within about 5 seconds.

Turbo X_J

Poor ground. Just an FYI, a code indicates a problem with a circuit, not necessarily a component. First step, disconnent the battery & clean all the grounds. Then hook the battery back up & see what you get.

Mark Bump

How do I reset the computer? I'm having the same high idle issue after replacing my iac

Jeepwalker

You might have bumped an old brittle vac line during the process and cracked it. Easy to do. High idle is common complaint on theses and most guys seem to find a bad vacuum somewhere. This is a situation where it would be very helpful to throw a cheap vacuum gauge on the engine and measure it. Mine measures like 15-ish at base idle but goes up to like 18 off-idle. I think the gauge I bought was $5 at a swap meet. Ensure the nuts on the front/rear of the intake are tight (they get loose). Your air temp gauge in the intake ...it's probably really carboned up too unless you've cleaned it lately.

Check the EGR valve and carbon deposits below it ...that can cause high idle too.
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Mark Bump

I cleaned the intake and the port where the IAC valve goes before I installed the new one. Did everything that I read and saw online and watched the videos on how do get it to reset, but nothing changed it still idles at 1800-2000 and even with my for off the accelerator the hell will speed up. I don't know if I did something wrong or if I was supposed to set the IAC valve pindle a certain way before installing. Going to take it out again today and start the whole process over again and see if I can get it to work right. Really wish I had someone around to help me lol

Jeepwalker

What I and others are saying is the IAC is only 'one' component that *can* cause high idle. Low vacuum is another very common source of high idle. Especially the old hoses from and around the valve cover or another vacuum leak (as outlined above). Consider putting a vac gauge on it to measure ..then you'll know for sure. EGR is another. So, while it's good to do what you've done, you also need to check off the other elements which can cause a high idle.

Idunno

Mine was a combo platter where the IAC and the O2 sensor were both failing. Truck idled poorly. I changed the IAC and got a big idle. Changed the O2 sensor and got the idle back. My replacement IAC was not adjustable.

Oswalla

It is entirely possible you bought a bad one. Double check your o-ring is in good shape on the iac, source of vacuum leak maybe. I am assuming you changed only the iac and problem started. Or the problem was a high idle before putting new iac on.

Spencer_P

To reset computer: Disconnect battery for 20 minutes and reconnect, idle for 2 minutes in park with AC off, 2 minutes in park with AC on, 2 minutes in gear with AC on, 2 minutes in gear with AC off.