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Thread: p38 revving issues.

  1. #1
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    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
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    What stepper motor would that be? Is this a gems or a bosch engine?

    -P

  3. #3
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    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

    2002 P38 Range Rover HSE

    Sequential LPG - Redarc Charger - TPMS - Ashcroft Locker
    Wheel Carrier - Bullbar & Spotlights - 285/75/16 BFG KM3’s
    On Board Solar - Stainless Snorkel - 2” Suspension Lift

  4. #4
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    That’s 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. I’ve seen my Mechanic do this to diagnose wether the MAF sensor was faulty or not. The only problem is i’m Not exactly sure which one of the two cable prongs you need to jump, as i wasn’t paying attention as to when my mechanic jumped the cables. Would anyone care to clarify this please?

  5. #5
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    +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
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    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
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    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

    2002 P38 Range Rover HSE

    Sequential LPG - Redarc Charger - TPMS - Ashcroft Locker
    Wheel Carrier - Bullbar & Spotlights - 285/75/16 BFG KM3’s
    On Board Solar - Stainless Snorkel - 2” Suspension Lift

  8. #8
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    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 ,,,,

  9. #9
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    Quote Originally Posted by prelude View Post
    What stepper motor would that be? Is this a gems or a bosch engine?

    -P
    its a gems

  10. #10
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    stepper motor is the ICV

    Quote Originally Posted by fabphil View Post
    its a gems

    ICV idle control valve ,,,,

    They get crap in them and get stuck ,, some times open some times closed ,,

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