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Old 01-28-2014, 09:36 AM
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Rough idle please help

Hi I have a 02 grand cherokee with roughly 160xxx miles on it and it has an unsteady idle and feels rough. It's idle back and forth between 550 and 650 rpms. What could be causing this?
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Old 01-28-2014, 03:51 PM
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Re: Rough idle please help

If you have the 4.7l a common fault is the throttle position sensor... but then it comes down to what exactly you mean. If the idle goes up and down, but runs alright you are likely looking at the throttle position sensor, if it runs poorly it could be any number of things, more symptoms would be required to help any further.
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Old 01-28-2014, 04:55 PM
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Quote:
Originally Posted by 2005JGC View Post
If you have the 4.7l a common fault is the throttle position sensor... but then it comes down to what exactly you mean. If the idle goes up and down, but runs alright you are likely looking at the throttle position sensor, if it runs poorly it could be any number of things, more symptoms would be required to help any further.
it runs really good. Just when I put it in park or let it idle that's when it starts
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Old 01-28-2014, 08:09 PM
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Re: Rough idle please help

The idle air control stepper motor probably needs to be cleaned. It sits under the TPS on the throttle body. Very well kn own to sludge up and give unstable idle.
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Old 01-30-2014, 09:53 AM
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Re: Rough idle please help

Both guys could be right, but I would start with Frango's suggestion. Get a can of carb/throttle body cleaner and pull off the resonator. Spray lightly in the throttle body and open it by hand to wipe up any sludge built up. Use a q-tip or a rag over a small stick to clean the idle air passage (under the main throttle intake) and also pull the idle air motor off the side of the throttle body, and carefully wipe off the tip. Be careful not to push or twist it, they are kinda fragile.

If you are still having problems check out the throttle position sensor, usually you will have more than just a rough idle with that but it could be just starting to go. If you have access to a scan tool with data logging plug it in and watch the TPS value, if it jumps around a lot with gentle pressure on the accelerator, your TPS is bad.

If you're still having problems, check to see if the spark plugs are starting to foul.
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