1200 rpm idle

[Jeepcruzer]

1998 Jeep TJ. I have replaced the TPS, IAC already. Issue I am having is that idles up when gas pedal is lightly tapped. Not even trying to rev it. Is this more of a vacuum issue that causes it to idle up to 1100 or 1200?
Thanks for your input.

I have also replaced the upstream and downstream O2 sensors.

 

[Gollywomper]

Yes could be a vacuum leak. Make sure your throttle linkage is returning all the way back closed as well.

 

[Jeepcruzer]

Yes could be a vacuum leak. Make sure your throttle linkage is returning all the way back closed as well.

Thanks for the advise. I will check those. But to confirm, are we talking about the throttle cable that attaches to the gas pedal? Also when I manually turn and rev the engine , the spring on the throttle linkage does goes back to its original position. Thanks GOLLYWOMPER….

 

[Jerry Bransford]

My bet is a vacuum leak. If you replaced the IAC after the rpms started going to 1200, it's time to chase the leak. Go buy a can of starter fluid or carb cleaner and after starting the engine, spray the vacuum hoses and their fittings. If the starter fluid or carb cleaner finds a vacuum leak it'll be sucked into the engine and the engine rpms will change. If you don't find it on top of the engine, there are more vacuum fittings plus the vacuum reservoir located under the battery tray.

 

[Jeepcruzer]

Briefly but normalizes itself if I leave the gas pedal alone for 5-7 seconds.

I did noticed the cable where it attached itself to the pedal have a slack. Is that suppose to be like that?

 

[Jeepcruzer]

My bet is a vacuum leak. If you replaced the IAC after the rpms started going to 1200, it's time to chase the leak. Go buy a can of starter fluid or carb cleaner and after starting the engine, spray the vacuum hoses and their fittings. If the starter fluid or carb cleaner finds a vacuum leak it'll be sucked into the engine and the engine rpms will change. If you don't find it on top of the engine, there are more vacuum fittings plus the vacuum reservoir located under the battery tray.

Jerry, thanks for that trick. I didn’t think of that. I will do that and let y’all know. Thanks

 

[Zorba]

Is this a "usta work" or a "never worked (since I've owned it)"? Check the CCV hookup. Make sure the correct elbow is on the back end of the valve cover - it has a restrictor in it. Or if there's cracks/looseness in its hookup as it is part of the vacuum system.

 

[Jeepcruzer]

Is this a "usta work" or a "never worked (since I've owned it)"? Check the CCV hookup. Make sure the correct elbow is on the back end of the valve cover - it has a restrictor in it. Or if there's cracks/looseness in its hookup as it is part of the vacuum system.

 

[Gollywomper]

Thanks for the advise. I will check those. But to confirm, are we talking about the throttle cable that attaches to the gas pedal? Also when I manually turn and rev the engine , the spring on the throttle linkage does goes back to its original position. Thanks GOLLYWOMPER….

Try applying a bit more return pressure where the cable attaches to the throttle body. If that seems good follow Jerry’s advice on a vacuum leak. Did this just start or always been there?

 

[Jeepcruzer]

Actually worked before. The gas pedal became a bit sensitive even with the slightest touch on the pedal, the engine revs up

 

[Gollywomper]

I had a similar issue when I bought my TJ. I had to increase the return spring pressure a little bit.

 

[Jeepcruzer]

Try applying a bit more return pressure where the cable attaches to the throttle body. If that seems good follow Jerry’s advice on a vacuum leak. Did this just start or always been there?

It just started after IAC replaced. Actually it was rough idling before IAC replaced. Then rough idling fixed after then noticed the high idle.
I also manually turned the throttle more than ten times and even sprayed lubricant on it just to ensure nothing was causing it to bind . Thank you for these advises

 

[Jeepcruzer]

I had a similar issue when I bought my TJ. I had to increase the return spring pressure a little bit.

How did you do that? Is there a YouTube of it. Where do I tighten the spring ? Picture or video swill help a lot

 

[Gollywomper]

Ok. If it started after replacing the iac then it is probably related what you did there. Loose or missing vacuum line or TB is sucking air.

 

[Jeepcruzer]

Ok. If it started after replacing the iac then it is probably related what you did there. Loose or missing vacuum line or TB is sucking air.

Thanks will check those later today. Much appreciated Gollywomper

 

[aston4]

I had to replace both IAC and TPS on my XJ with the same fuel system to fix similar problem. Replaced one, can’t remember which, still problem, replaced other, no problem. It was like $30 for both at whichever random parts store.

 

[CharlesHS]

It just started after IAC replaced. Actually it was rough idling before IAC replaced. Then rough idling fixed after then noticed the high idle.
I also manually turned the throttle more than ten times and even sprayed lubricant on it just to ensure nothing was causing it to bind . Thank you for these advises

I would check the IAC to ensure the O ring is not cracked or rolled and that the IAC is seated properly...
Either could cause a vacuum leak that may affect idle RPMs.
The procedure that JB suggested may assist you in determining IF the problem is with the IAC.

 

[Jeepcruzer]

I had to replace both IAC and TPS on my XJ with the same fuel system to fix similar problem. Replaced one, can’t remember which, still problem, replaced other, no problem. It was like $30 for both at whichever random parts store.

Both were replaced already. I sprayed some throttle body cleaner where the linkage is and it seemed to revved up engine. I’m beginning to think it’s the rod that opens and close the valve in that throttle body

 

[CharlesHS]

Both were replaced already. I sprayed some throttle body cleaner where the linkage is and it seemed to revved up engine. I’m beginning to think it’s the rod that opens and close the valve in that throttle body

When you replaced the IAC; did you clean the seat inside the cavity where the IAC disc seats against ?
Gunk on the seat or a partially obstructed IAC bleed port in the throttlebody throat should be looked at....

 

[1Salty Dawg]

Both were replaced already. I sprayed some throttle body cleaner where the linkage is and it seemed to revved up engine. I’m beginning to think it’s the rod that opens and close the valve in that throttle body

Curious if it is the little O ring on that shaft that maybe dry rotted and is now letting in a little air. There is a fix for that somewhere on the interweb. Google it.