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-   -   Rough idle with RPM drop (http://www.jeepgarage.org/f203/rough-idle-with-rpm-drop-58786.html)

southernfryedyankee 04-21-2013 12:28 PM

Rough idle with RPM drop
 
I have been having an issue where my jeep idles fine then for some reason the RPM's drop and the idling gets very stumbly causing the car to tremor. I have had no issues with driving the car, this only happens when the car is stopped. My average idle speed is around 700 RPM but easily drops down to around 500-600 when the car has stopped, it corrects itself then happens again without warning. I am considering a vacuum leak but if it was a vacuum leak wouldn't it happen more consistently with a continuous stumbling idle? I have a 99 JGC I6 2WD

Frango100 04-21-2013 05:05 PM

Re: Rough idle with RPM drop
 
Did you check the throttle body if its dirty inside? Also the IAC stepper motor plunjer gets dirty over time and can cause idle problems.
Could eventually be a TPS which is on its way out.

southernfryedyankee 04-21-2013 08:49 PM

Re: Rough idle with RPM drop
 
I made a video, maybe it will help. I replaced the TPS around a year ago. If the rubber coupler seal from the resonator to the throttle body is broken could that create a vacuum leak and cause my symptoms?

99 Jeep Grand Cherokee stumbling when RPM's drop. - YouTube

Frango100 04-21-2013 09:44 PM

Re: Rough idle with RPM drop
 
When you select the AC on, the PCM gets a signal to increase the rpm a bit. This is to prevent that the rpm would go down too much due to the load of the AC compressor. With the AC compressor off, is it still doing the rpm drop?

southernfryedyankee 04-22-2013 03:34 AM

Re: Rough idle with RPM drop
 
Unfortunately yes it does

Quote:

Originally Posted by Frango100 (Post 808844)
When you select the AC on, the PCM gets a signal to increase the rpm a bit. This is to prevent that the rpm would go down too much due to the load of the AC compressor. With the AC compressor off, is it still doing the rpm drop?


Frango100 04-23-2013 09:24 AM

Re: Rough idle with RPM drop
 
When it was a vacuum leak, the problem should be constantly.
Did you check the IAC stepper motor and the throttle body for dirt ont he throttle blade?
Did you check if the problem also happens in Park or N?


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