High RPMs when shifting (and cold)

EvilRbt

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Ever since I cleaned out my TB to solve sticky throttle issue, I’ve had a new problem…

Btw, 1992 YJ 2.5L

The RPMs go to 2000 when shifting or pressing gas pedal, before dropping back to normal.

I don’t see any disconnected vacuum lines. I replaced the IAC. Kinda stumped. Was running fine before I removed TB and I replaced the gasket.

Could it be as simple as not torquing down the TB bolt enough? I thought they just had to be firm, not too tight.

Thinking I’ll have to take into a shop and get the vacuum system tested.

Any suggestions? Thanks!
 
Do you still have the original IAC to put back in or did it completely fail? Also that sounds typical ov a vacuum leak. Try spraying the lines with carb cleaner at idle and listen for an rpm change.
 
I tried spraying TB cleaner around vacuum connections and no change in idle. I took it by a mechanic (who knows jeeps) and he suggested I change IAC again as the “new” one I got might be junk. This one is gold and he said get a black one.

I DID keep my old one (which is black). I may clean that up and give it a shot before dropping another $50+ on another new IAC.
 
Hate to say this but on my 91 ive tried 3 different IAC's including a Mopar one and it idles at 1100 most of the time and has been like that for 2 years now. . Unfortunately I trashed the original one or Id put it back on. Problem there was it idles at 500 rpm. Be nice to hear what you come up with if you correct your problem.
 
Strangely enough, yesterday I was working on a 2008 Jeep Patriot which had an engine code for possible vacuum leak. All the hoses check ok when I sprayed them but then I gave a shot at the fuel injectors and that's when the engine stumbled at idle.

Short story is I replaced the old, hard O-rings on each injector and it stopped the leak. I cleared the codes and now everything checks ok.

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Hate to say this but on my 91 ive tried 3 different IAC's including a Mopar one and it idles at 1100 most of the time and has been like that for 2 years now. . Unfortunately I trashed the original one or Id put it back on. Problem there was it idles at 500 rpm. Be nice to hear what you come up with if you correct your problem.

I’ve read similar statements before. Why do so many IACs seem like junk?

Also, did you adjust them before installing? I tried putting my old IAC back in yesterday and the tip isn’t the screw type so I pushed it in (I read it needs to be under 1 1/8 inch). Once I fired up the Jeep, the RPMs were higher than ever.

This whole situation is such a brainscratcher. The Jeep idled just fine before I cleaned the throttle body (just sticky throttle).

I’ve ordered another IAC. Before it arrives I think I’m going to disconnect the battery overnight to fully ensure everything resets.

Would love to solve this issue obviously. Someone elsewhere claims that if it only happens when cold, it’s gotta be a vacuum leak.
 
You may have done this, use a Q-tip with cleaner and swab the inside where the IAC piston seats. There is often a build up of gunk that causes the poison to stick.
 
Yeah I cleaned it out thoroughly.

Wondering if I should try changing the TB gasket. I bought a new one from O’Reilly when I first cleaned the TB but maybe it’s flawed.

Really perplexing issue.

Anyone know if replacing the TPS would impact the idle between shifts/ when cold?
 
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Spraying carb cleaner around gasket on the base of the throttle body will let you know if there's any leak.

On a cold engine try spraying along the intake gasket between the manifold and head.
 
Spraying carb cleaner around gasket on the base of the throttle body will let you know if there's any leak.

On a cold engine try spraying along the intake gasket between the manifold and head.

I tried that and couldn’t see/hear any difference.

Anyone know how long the battery should be disconnected to reset the ECU? I only had mine disconnected for the 10-20 minutes it took to swap out the IAC. Wondering if that wasn’t long enough so I’m leaving the battery disconnected overnight.
 
Overnight would more than do it.

Just fired it up to check if draining the power would help the new IAC reset... nope, no difference.

I have another new IAC coming in the mail. If that makes no difference, it's gotta be a vacuum leak but absolute mystery where it's located.