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Old 09-17-2010, 04:15 PM   #1
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Question Jeep shakes on startup!

I just had a new engine installed and everything was fine for about a month and now every morning when I start it up, it shakes for about 10 seconds and then mellows out. I know that the engine was reprogrammed for the install at the shop and everything that was originally on it was put back on. The spark plugs are relatively new but the injectors are original. What could be causing this?

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Old 09-17-2010, 04:20 PM   #2
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Does it idle really low when first started? That can cause the shaking you are describing.

Just the first thing that came to mind because I had a old plow truck that did the same thing, I never bothered to figure out what caused it to idle low at start up since it was a plow truck and wasnt worth the effort.

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Old 09-18-2010, 03:09 PM   #3
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Yes it idles below 1000rpms fro a few seconds but then jumps up to normal. I was reading somewhere about how an EVAP leak from the EVAP Canister can cause a rough idle. I was told that a simple test for this is to use a pair of long-nose pliers to squeeze the main purge line shut while the engine is idling. There should be no change in the idle. If there is, you need to buy a new one. Does anyone know where the main purge line is and where the EVAP Canister is?
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Old 09-18-2010, 03:33 PM   #4
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I am also getting a code PO456 and I smell a light gas smell coming through the vents when I start it up.
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Old 11-11-2010, 09:00 PM   #5
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I have the opposite issue. My engine shakes when I turn it off. I thought it was the engine mounts but the mechanic at the Jeep dealer didnt seem to concerned with it.
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Old 12-22-2010, 04:05 AM   #6
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If you guys get any more information, please share. My Jeep sometimes shakes at startup and always has the P0456 engine code. Runs good though.

John

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