99 jeep 4.7 rough idle when stopped in drive - JeepForum.com
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post #1 of 3 Old 04-19-2012, 07:31 PM Thread Starter
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1999 WJ 
Join Date: Apr 2012
Location: Altoona
Posts: 5
99 jeep 4.7 rough idle when stopped in drive

Hello Jeepsters my 99 grand cherokee limited when at operating temperature stopped in drive the idle goes from 750rpm to 400rpm or lower like its going to stall. Tried this in reverse and the rpm stays at 750. Replaced fuel filter, AIC motor, cleaned throttle body, oem spark plugs. Put on snapon computer, misfire #6 so I replaced coil. No more misfires, still the same problem. Could not find no more bad readings. Maybe the TPC? Any suggestions!!! Thanks

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post #2 of 3 Old 04-19-2012, 07:44 PM
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2007 JK Wrangler 
Join Date: Jan 2005
Posts: 652
Hi there, welcome to the forum.

This post will probably be moved, because it really belongs in the tech section for your model. You're probably not going to get much for responses in this forum.

Second I think we need to sort out what you're jeep is. XJs didn't come with the 4.7. So you either have an XJ with a 4.0L inline 6, or a WJ Grand Cherokee with the 4.7 V8.

If you do have a WJ with the 4.7, I would pull the spark plug and see if it looks like there's been coolant burning in the chamber. The plug will look pretty clean compared to others and in my experience the electrode had a white "crackly" film on it, not something that looks like a powder which can be normal. I had this happen to me, started as a misfire and ended with a head replacement. Of course, it could be some other extremely simple thing.

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post #3 of 3 Old 04-19-2012, 07:54 PM Thread Starter
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1999 WJ 
Join Date: Apr 2012
Location: Altoona
Posts: 5
Thanks for the welcome. Plugs are burning excellent, runs like a beast when on the gas. Just bad when stopped in traffic.
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4.7 liter , idle problems , jeep , rpm

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