98 TJ Idle issues

[Guest]

Hello,

I have read through all of the idle threads I could find with no luck so hoping someone can help.

98 TJ idles high. But the behavior is different than what I expect as it is not consistent and seems backwards.

My Jeep is garaged so does not sit out in cold weather, when I start the jeep in the morning, it idles fine, in the 700-800 range most of the time. When the jeep comes to temp, is when the high idle starts. On occassion, the jeep will idle just slightly high (100 rpm range) at start up.

After driving for a while, if i shut off the Jeep and restart it a few minutes later, it will idle ok, even if still hot. After driving it will idle high again.


I have done the following:

Replaced manifold gasket
replaced IAC with a new one
Replaced coolant temp sensor
cleaned entire throttle body


not sure what else to do.

[jagular7]

Sounds like a vacuum leak.
Check the throttle body bolts to manifold, wiggle the vacuum hoses off the intake.

I had issues recently on my 99 4.0l TJ. It was inconsistent. Wouldn't start for my daughter at night. I got it started but wouldn't idle till it got warmer. I just cleaned the tb with injector cleaner and it appears to have better quick starts (was starting fast already) and idle. No issue yet for non-starting. No CEL came up either.

[Guest]

Thanks Mike,

I have checked the manifold and throttle body bolts. They are all tight. I have looked at all of the vac lines but cant find anything that looks to be a crack or leak. Doesnt mean there isnt one. I guess next step would be to smoke test this thing. Only reason I dont think its a vac leak is because of the wierd behavior. I would expect a slight high idle when cold but this is opposite. Usually idles fine at start and then after driving starts to high idle.

On most occassions, I can turn the jeep off and start it 5 min later while still hot and it will idle fine. Once I drive again, back to high idle. It is really only idling around 1200-1300, highest it has gotten is 1500 range so its not going crazy. Just annoying the **** out of me at this point, lol.