Random high idle after replacing IAC

[Ethan.diefen]

Hello all, I’ve been having an issue with my 1997 TJ, 4.0 manual that I bought a few months ago

The Jeep runs perfectly while driving, but it has had idle issues since the day I bought it. At first, the idle would bounce around between 800-1100 rpm. I replaced the IAC with one from Autozone, and it began idling at 4000 rpm and wouldn’t go below 3000 even after driving at highway speeds for 20 minutes and leaving the battery disconnected overnight. Put the old IAC back in, and cleaned the throttle body with carb cleaner. The surging idle immediately went away, but began holding a steady idle at about 300 rpm and felt like it was on the verge of stalling.

Yesterday, I bought another IAC from Advance Auto and cleaned the throttle body a little bit more before installing it. After cruising at about 50mph for a little bit, the idle settled down to a steady 750 rpm. I thought that would be the end of it, but I stopped at the store on the way home and when I started it up afterwards it began idling at about 1200, but would occasionally idle at 750. Today, it’s doing the same thing. First light I came to it idled at 1200, then the next one it was at 750, and then back up to 1200. Doesn’t seem to be any pattern to it.

Then this afternoon, it began idling at 2000 rpm when I was on my way to lunch.

I replaced the TPS when I replaced the IAC the first time, short of ordering a genuine MOPAR IAC, I’m at a loss of ideas for what the issue might be. I’m planning on leaving the battery disconnected tonight and seeing if that makes any difference.

 

[Jerry Bransford]

Stop installing store brands for critical devices like sensors, IACs, etc. Store brands are fine for floor mats and air fresheners but nothing critical. Before I learned that I had to buy THREE Duralast oil pressure senders one Sunday from Autozone before I finally got one that worked properly. All had the same part number but only one worked properly. One of them actually worked backwards, giving a high oil pressure indication at idle rpms and dropping lower as I revved the engine. Store brand sensors are JUNK.

And clean the IAC's air passages inside the throttle body too. That can only be done while spraying TB cleaner into the throttle body while the engine is running at idle rpms. The cleaner will flood the IAC so the engine will die but that's fine and actually gives the cleaner more time to work on the gunk that has built up. Just start the engine and do it again, and again, and again. I don't stop spraying the TB cleaner into the TB at idle rpms until at least 1/3 of the can has passed through the IAC and its air passages.

 

[Ethan.diefen]

Stop installing store brands for critical devices like sensors, IACs, etc. Store brands are fine for floor mats and air fresheners but nothing critical. Before I learned that I had to buy THREE Duralast oil pressure senders one Sunday from Autozone before I finally got one that worked properly. All had the same part number but only one worked properly. One of them actually worked backwards, giving a high oil pressure indication at idle rpms and dropping lower as I revved the engine. Store brand sensors are JUNK.

And clean the IAC's air passages inside the throttle body too. That can only be done while spraying TB cleaner into the throttle body while the engine is running at idle rpms. The cleaner will flood the IAC so the engine will die but that's fine and actually gives the cleaner more time to work on the gunk that has built up. Just start the engine and do it again, and again, and again. I don't stop spraying the TB cleaner into the TB at idle rpms until at least 1/3 of the can has passed through the IAC and its air passages.

I agree, I try to stay away from parts store parts whenever possible, but I haven’t been able to find the proper OEM IAC. The original one I removed has “53007562” on it, but I can’t seem to find that exact part number for sale anywhere.

The way you described cleaning the IAC and TB is exactly how I had originally cleaned it.