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Rough idle but good compression while engine running

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  • [Corsa C] Rough idle but good compression while engine running

    Hi all.

    Just came back from a failed MOT with my Corsa C 1.2 Z12XE and the mechanic told me I could have a bent valve. Idle is rough as mentioned in the title. I have changed the spark plugs prior to the MOT and that was not the issue. The mechanic also told me that the coil pack can't be the issue as when the engine is running, there is no misfire.

    Got the following codes: and their states

    P0340-9 camshaft position sensor circuit malfunction - present
    P0300-8 random multiple cylinder misfire detected - invalid
    P0303-8 cylinder 3 misfire detected - invalid
    P0302-8 cylinder 2 misfire detected - invalid
    P0300-2 random multiple cylinder misfire detected - invalid
    P0303-2 cylinder 3 misfire detected - invalid
    P0304-2 cylinder 4 misfire detected - invalid
    P0302-2 cylinder 2 misfire detected - invalid

    Any help is appreciated
    Last edited by 2jzCorsa; 11-01-2018, 04:57 PM.

  • #2
    How have you done the compression test with the engine running? You can't have a bent valve if you've have good compression. Possible causes could be.
    Chain to slack or jumped.
    Coil pack
    Cam or crank sensor.
    Or check the small earth wires (brown colour ) that are bolted on a small plate on top of the gearbox and there's also one thats bolted to the ecu.

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