1. #1
    Rsnyder22's Avatar
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    99 grand cheeroke extreme high idle 5k rpm

    Needing help got a 99 grand original motor quit after #4 piston cracked in half bought a used 4.0l motor 2003 jeep grand and installed it on start up eng. Revs up to 5k rpm and stays new timing chain trottle body sensors new cam sensor new crankshaft sensor. New ecm comupter No noticable vaccuum leak or air intake this gots me stumped on whats next to try.

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    A vacuum leak is most likely. At the cylinder or the throttle bottle even a crack away from the engine. Like the vac resivoir under the battery. Second a bad or dirty IAC on the TB.
    Is there any sputtering or popping? If so it could be at a cylinder like the intake not married or bent or the gasket leaking from exhaust to intake. Even the or ing gaskets on the injectors.


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    Re: 99 grand cheeroke extreme high idle 5k rpm

    To add to colleagues suggestions
    Check for codes.
    Confirm throttle is closed

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    2 New sensors on throttle body eng dies out with tb closed

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    OK this is a replacement engine - in a 1999 GC,

    WHat ECM is installed the 99 or a 03?
    What codes are showing?
    What sensors and why?
    Wil eng start with TB closed?

    As mentioned knee jerk would be a vacuum leak - throttle stuck open..


    NOW you mention - Having TB open this suggest over fueling - check inj wiring - easy test with noid light or test light KOEO. Also heck fuel pressure regulator for fuel in vacuum line.

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    Quote Originally Posted by Rsnyder22 View Post
    2 New sensors on throttle body eng dies out with tb closed
    I take it you mean the TPS and IAC.

    I think the TB is closed on start. The IAC controls the airflow at idle.
    If you stall at idle with the TB closed your IAC is not connected properly, dirty or stuck.


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    Re: 99 grand cheeroke extreme high idle 5k rpm

    The TB is closed at start, opening a TB gives the engine AIR suggesting it is overfueling,
    Checking codes would ID a IAC wiring issue....and many other systems.

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    Pull and inspect your plugs. Post pics of the plug tips before you clean or wipe....


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    Re: 99 grand cheeroke extreme high idle 5k rpm

    I had that happen after spraying down the engine for its annual cleaning . Moisture in a plug connection . Took the ones around the throttle body apart , sprayed them with contact cleaner , let them dry , plugged them all back up . Problem solved .
    Also was already mentioned , the IAC is maybe stuck . They carbon up . Spray cleaner in the port . Most time you don't even need to take the untit out to clean it . There's just enough build up in there to make it stick . It might need more but I'd try that first .
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    Re: 99 grand cheeroke extreme high idle 5k rpm

    2 new sensor on TB

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    Re: 99 grand cheeroke extreme high idle 5k rpm

    Quote Originally Posted by JPNinPA View Post
    I take it you mean the TPS and IAC.

    I think the TB is closed on start. The IAC controls the airflow at idle.
    If you stall at idle with the TB closed your IAC is not connected properly, dirty or stuck.


    JPNinPA
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    No stall

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    99 grand cheeroke extreme high idle 5k rpm

    Did you spray around the intake, TB, injectors, plugs and vac lines with carb cleaner or WD40? If you spray with the engine running and the idle changes you just hit a leak.


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    Last edited by JPNinPA; 09-15-2017 at 10:28 AM.
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