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Old 09-20-2011, 09:45 AM
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Grand Sherokee 2001-idle problem

Hi, I have a 2001 G Cherokee LTD 4.7l. When I start the engine the Idle goes up and down between 1200rpm to 2000rpm before guetting down to about 900 rpm after a couple minutes. When hot, if I put it from drive to park, the rpm goes up to ±2800 rpm and stays there. Cause of that, the transmission does not work well neither. Last year, I took my Jeep to the dealer for that problem. They told me they could not figure out what was the problem ! Any suggestion !!! Thanks
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Old 09-20-2011, 09:49 AM
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Re: Grand Sherokee 2001-idle problem

Unstable idle is often caused by a dirty Idle Air Control passage. The best is to clean the whole throttle body. Take the IAC stepper motor of as well to clean well the plunjer and the air passage. When cleaning the plunjer, take care not to put too much rotational force on it, or otherwise the plastic pieces that should keep it from turning, will break off and you have to buy a new IAC motor (how do i know this). Also don't let throttle body cleaner go into the IAC motor, keep it with the plunjer down. After mounting back all the parts and connecting the negative battery cable, the PCM (powertrain control module) will move the stepper motor to both end stops to relearn these positions. See also this previous thread with some pictures of how it looks like: Lopey idle on an 02' Overland / 4.7HO
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Old 09-21-2011, 02:06 AM
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Re: Grand Sherokee 2001-idle problem

Quote:
The throttle position sensor is a VERY common failure on the 4.7l that causes irratic idle amongst other things...

If you grab the sensor with the car running and give it a jiggle (obviously its not going to move much with the two T20 torx holding it) but just try to move it around a bit. If your idle fluctuates as you do this replace the sensor.
Quoting this from another post I just made in the wj section for a similar concern.

The problem is that unless you know the jiggle trick or are using a labscope on the throttle position sensor I dont think you can actually see the problem. Considering it rarely throws a TPS code, if you have no code to point you in the right direction and no labscope and dont know the little jiggle trick I said in the quote then it turns into "no problem found".
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Old 09-27-2011, 12:43 PM
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Re: Grand Sherokee 2001-idle problem

Thanks for the tips. I cleaned the idle stepping motor and the throttle body. Big improvement. Now when I start the engine, the RPM settle to arround 700 RPM and remain stable. But once hot and running, the RPM goes up and down. I thought replacing the throttle position sensor. Thanks again
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Old 09-27-2011, 04:48 PM
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Re: Grand Sherokee 2001-idle problem

Yes, as 2005 JGC also recommended, thats probably due to a bad TPS. Easy to change and not so expensive.
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