TJ won't return to idle speed

Philip

Philip

Member
Joined
Jan 2, 2017
Messages
43
Location
Apache Junction, Arizona
My Jeep does something weird. Some times when you lift off the gas, it spools down to 1500 rpm EXACTLY and stays there for a second or two before returning to idle speed. When it decides to do this, it does every time you lift off the gas from the moment you start it until the moment you turn it off. If it doesn't do it from the start it does it not at all. Some times it will do it several days in a row then not do it again for a month. Check engine light does not come on ands it's not throwing any error codes. Nothing appears amiss at the throttle body and the peddle is fine. Sitting in the driveway the symptoms are as I've described. When driving it feels like there is excessive lash somewhere in the drivetrain. PITA to diagnose because you don't know when it's going to happen and, of course, it doesn't happen when it would be convenient to work on.

Oh, yeah, 2004, 4.0, 5 Spd.

This seem familiar to anyone?

Philip
 
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How many miles on the engine ?
Have you done any work on the engine recently?
x2 with @Imapepper reply
With no codes thrown and with the problem showing itself with no pattern, I would first check the torque of all intake and exhaust bolts.
Check normal stuff you can see like electrical connections around the throttle body.
If the engine has high mileage consider replacing the intake/exhaust gasket and torque to specs.
It's hard to diagnose inconsistent engine problems :-/ just watch for any patterns like hot weather for example that might trigger the high idle
 
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It may be quite simple, if you're lucky. If you use footwell mud liners or other slideable inserts, your driver side one can creep forward and interfere with the return of the gas pedal, which can give you symptoms as you describe. I've also had a runaway engine from that cause.
 
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