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Thread: p38 revving issues.

  1. #1
    Join Date
    Jan 2018
    Location
    adelaide
    Posts
    1

    p38 revving issues.

    hi i've had my p38 for 5 yrs never missed a beat just recently i replaced the cam and lifters as it was getting sluggish and noisy it ran fine for a few days then started revving to 2000rpm all the time until you put it in gear then would drop to around 1000 rpm. i replaced the stepper motor and it didn't make any difference any advice as to what the problem could be. phil

  2. #2
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    146
    What stepper motor would that be? Is this a gems or a bosch engine?

    -P

  3. #3
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,480
    I could throw parts at you, as lots of people could. Sometimes high idle is due to the ECU seeing an incorrect temperature reading. How long since you sprayed the MAF sensor with a bit of cleaner? Cheap and easy to do, could eliminate something.

    Cheers
    Keithy

  4. #4
    Join Date
    Aug 2010
    Location
    Pakenham
    Posts
    579
    Thatís what I reckon too. MAF sensor giving incorrect readings. There is a reset procedure that you can do by disconnecting the sensor lead and jumping two of the three cables on the lead. This apparently resets the MAF settings. Iíve seen my Mechanic do this to diagnose wether the MAF sensor was faulty or not. The only problem is iím Not exactly sure which one of the two cable prongs you need to jump, as i wasnít paying attention as to when my mechanic jumped the cables. Would anyone care to clarify this please?

  5. #5
    Join Date
    Oct 2007
    Location
    Williamstown, Victoria
    Posts
    578
    +3 on the maf, I was wondering the same thing, as Keithy and Redlandy said, it does sound like incorrect values being fed to the ECU.
    I had a maf sensor go bad causing rough idle, cleaning didn't help, but a new one did wonders.
    If you try cleaning it, make sure you use the correct maf cleaning spray.

    I once read about resetting the adaptive values for the EFI system using Faultmate/ Nanocom, might be worth exploring if cleaning has no effect.

  6. #6
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    10,664
    The speed of idle of the engine depends largely on the throttle plate/butterfly. That is why it is called a throttle.

    Extra air can cause I high idle via the stepper or air leaks after the throttle plate.

    The MAF controls idle mixture only, and can cause rough rich or lean idle but cannot cause a fast idle.
    Regards Philip A

  7. #7
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,480
    An incorrect temperature or flow reading from the MAF will cause the idle stepper motor to open longer, running a high idle, and also run a richer fuel mixture, causing the idle rpm to change.

    Cheers
    Keithy

  8. #8
    Join Date
    Oct 2017
    Location
    nowra
    Posts
    60

    my 2 bob is

    You have a air leak into the plenium ,,, could be a cracked hose into the manifold ,,

    Best way to test ,,
    Get a can of WD40 ,,,Put the long plastic squrt nossle on ,,

    START THE RR ,, Spray the WD40 around all the joints of the intake manifold , vac pipes every where
    If the NOTE of the motor changes ,,,thats where the air is leaking into the intake ,,,,

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