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Old 01-03-2012, 03:55 PM
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Rumbling issue when JGC is idling or in neutral

Hello all, My JGC is 2 wd, inline 6, 165k miles. I have noticed that over the last few months my JGC is rumbling/shaking when I am parked with the engine running in drive or in neutral sitting stationary. Someone made mention that their could be carbon buildup around my throttle body plate so I completely cleaned that but also noticed the round gasket that goes between my throttle body assembly and air intake body is broken and I need to replace it (wasnt sure if that could be the culprit) Someone had mentioned it could be a damaged motor mount but I have no idea where it is located or what it looks like. I am not receiving any check engine lights. I also noticed today that when I started my car to go to work it was making a grinding noice and after a few of my car people looked at it they believe the bearings in my serpentine belt tensioner is on its way out as they said it looked like it was vibrating more than it should be, today was the first time it ever made any kind of grinding noise. My engine idles around 650-700 RPM when warm but around 1000 at startup and there is usually less rumbling/shaking at the higher idle RPM's

Any help or advice would be greatly appreciated.
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Old 01-03-2012, 04:03 PM
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Re: Rumbling issue when JGC is idling or in neutral

I would like to add that I changed my spark plugs about 2 months ago but not the ignition coil with the wires or wires themselves.
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Old 01-03-2012, 09:25 PM
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Re: Rumbling issue when JGC is idling or in neutral

A broken gasket or seal between the throttle body and air intake for sure can cause problems, not sure however if the engine would start shaking. Would suspect a higher idle. Did you also clean the Idle Air Passage in the throttle body and the idle air control motor plunjer? That one will cause inregular idling.
Your engine mounts are the rubber fittings where the engine is hanging in.
The serpentine belt tensioner pulley bearing becomes dry after a long time of use, causing it to wear quicker and it will be making noise. In worse cases, the bearing can block and the serpentine belt will break. So if its the bearing, better to replace it.
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Old 01-12-2012, 07:51 AM
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Re: Rumbling issue when JGC is idling or in neutral

Thank you Frango, i will be replacing the pulley ASAP. I notice the Jeep runs very smooth at first startup when engine has not had the chance to warm up. Idling at startup is around 1000 RPM and seems to be great but once the Jeep starts idling at 650 that is when the rumbling starts.
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Old 01-12-2012, 07:47 PM
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Re: Rumbling issue when JGC is idling or in neutral

Was the jeep already giving the problem before you changed the spark plugs? I donīt know the year of your jeep, but the newer engines donīt have ignition wires, but an ignition coil assy with 3 coils. Did you use the standard Champion plugs? And how is the air filter?
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Old 01-12-2012, 07:53 PM
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Re: Rumbling issue when JGC is idling or in neutral

The jeep had been rumbling prior to the change, someone recommended I change the plugs but the jeep still had the same issue. To be honest it may not even be an issue, it might just be me. I have the ignition coil assy with the 3 coils. I used the bosch plugs and I just changed the filter about 5-6 months ago.
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