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Old 12-04-2010, 03:24 PM   #1
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Question New Engine w/ rough idle

Hi guys,

So I've had a new engine installed and I recently have been having idling problems. It always starts up just fine but revs up to 1200rpms by itself and then drops below 1000 and the jeep starts shaking like its had a misfire. This happens even when I start driving. I'll pull up to a stop light and watch the rpm gauge continue to rev up by itself while I'm holding the brake harder and harder to keep the jeep from driving off on its own. Another issue when I am driving is I get a very high pitched whistle when ever I give it more gas. If I let off the gas slightly, it goes away. Lastly, If I am driving on the highway and I get above 60mph, the engine misfires. I can shut it off and turn it back on and it runs fine. Here is a list of what I have already replaced:

-2 upper O2 Sensors and 1 lower O2 Sensor (ordered the wrong one)
-Throttle Position Sensor
-Crank Position Sensor
-Spark plugs

Note: I have also gotten codes for a small EVAP leak and will be purchasing a new EVAP System soon.

If anyone could help me diagnose this one I would greatly appreciate it.

Thanks!!!

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Old 12-04-2010, 03:58 PM   #2
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Im not sure but it sounds like you may have an air leak on the manifold or under the throttle plate. The engine is trying to compensate for a reading one of the sensors is telling the ECM is not right thats why its speeding up. You can start the engine and spray WD-40 or carb cleaner where the intake meets the head it may help you find the leak the engine will smooth out for a moment if you put lquid in an air leak. Its worth a shot.

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Old 12-04-2010, 04:22 PM   #3
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OK, I'll try that. I did notice however when I changed the TPS that the gasket for the throttle body was this very cheap looking and very thin piece of brown paper. Are there better ones out there?
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