Topic: Very High Idle - need help!

[YellowTJ]

Okay, here’s the story. I have a 2000 TJ, 2.5L I4. Was working on putting on a turbo, when I ran into some smoking issues out of the tail pipe. In short, I bypassed the turbo and went back to a stock setup and it persisted. I ended up replacing the head gasket and put everything back together. Everything looked really good within the block. After I got it back together, went to fire it up and immediately started idling very high, around 3,000 rpm.

So started tinkering, checked all the sensors at the intake, and even replaced them actually (Mopar brand). Then checked all the vacuum lines, and replaced anything that even looked questionable. Even pulled the TB and reset a new gasket there. But my problem still persists with a high idle of about 3,000 rpm when I fire it up.

When I do fire it up it does sound like it runs smoothly. So I’m now at a point of not sure what to try next. Any suggestions?!?

[Jeffy]

I'm gonna guess a vacuum leak somewhere on the intake.

[95 Lowbuck]

Maybe the idle air valve?
Unplug it see if it makes a difference.
May sound obvious, but is the butterfly closed completely?

[YellowTJ]

Long time since this post, but wanted to follow up with the result. Did a smoke test to learn there was a leak at the intake manifold. This was due to the larger flange on the new exhaust header, and since it shares the bolts to cinch down to the head, the slightly thicker flange wasn’t allowing a tight enough seal at the intake manifold, hence the leak. Machined the face of the flange on the exhaust header down, which helped, but ultimately had to machine the upper face at the bolt locations to get it exactly right. Right connection, new gasket, no problems.

Lesson learned, even though it seemed tight and snug, this precision was down to .001” tolerance to really get it right. Thanks everyone for the input.

[Jeffy]

Nice!  Yeah, the flanges can be a place for leaks.  Some of them can be thicker causing problems.