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PT Turbo Idle speed

Discussion in 'PT Cruiser' started by george w, Jun 18, 2017.

  1. george w

    george w Member Level III Supporter

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    How is it possible to set the curb idle ( while in gear ) slightly higher, say 100 rpm, than the factory specified idle on a 2005 PT GT ? The car runs fine, but exactly at the normal curb idle there's a vibration resonance in the car body and the radio antenna quivers wildly. Just touching the gas pedal to bring the idle up a touch makes everything go away.
     
  2. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    Idle speed is controlled by the PCM. The 'minimum air' set screw is not an idle speed adjustment and shouldn't be tampered with. I would look at the possibility of worn or bottomed motor mounts first.
    The right in-frame mount on the turbo has been known to leak 'hydrostatic' fluid if it is a fluid-filled mount.
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  3. george w

    george w Member Level III Supporter

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    I know the drill about the minimum air adjustment on the throttle body and I know the PCM controls the idle speed with input from the a/c system and, I think, the power steering pressure sensor. Both the upper and lower motor mounts were replaced about two years ago but the price the dealer quoted to check/replace that middle mount was crazy, over $ 1000 ! They said something like the engine has to come out or at least it's as much work as taking the engine out. They did not indicate that the middle mount was bad when the upper and lower mounts were replaced but they did imply that the difficulty was high and time consuming. I will say that the motor mounts and those lower control arm bushings sure don't last very long.

    The car has the generic Chrysler PCM that was installed after the original PCM started throwing erroneous O2 sensor codes even though it has always run perfectly. It seems that these otherwise nice, but not very valuable, little cars typically need parts replaced that regularly wear out or fail well short of what one would expect the normal service life of such parts would be. The cost ( parts and labor ) drives these PT's to be scrapped at an early age.

    Can this generic PCM be programmed to kick the idle speed up a notch or "tricked" somehow like by shorting or modifying the power steering pressure sensor/switch ? Apparently these replacement PCM's are dumb until programmed. You would think that the idle speed could simply be set higher. Just raising the idle speed with the gas pedal a little bit clears everything up. Once off idle the car just purrs along.
    Maybe there's a "tuner" out there that can do it.
     
    Last edited: Jun 19, 2017
  4. pt006

    pt006 Member

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    I'm not familiar with the generic [blank- one size fits all] replacement PCM other than it must be programmed to a specific vehicle. It is possible that they did not program it properly when they installed it. ----- I.C. would know more.
     
  5. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    Programming of the blank Mopar PCM is done by part number for its intended application. It would violate Federal EPA law if the wrong computer program was used on a vehicle. The programming procedure is pretty simple and foolproof at the dealer. It will install the correct software as long as the correct procedure is followed.
    I don't think that you can get away with fooling the computer on idle speed. If it saw the P/S switch 'on' all the time, it might set a fault code.
    I do remember the time you had with the O2 codes a while back. I don't think that the computer is the cause of the idle problem.
    Is the idle vibration better or worse with the A/C on? Finding the real root cause of the slow/rough idle issue would be better than trying to band-aid it.
     
  6. pt006

    pt006 Member

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    See, I told you that I.C. would know more!
     
  7. chuzz

    chuzz Active Member

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    The middle mount is quite often the most over looked one because of it's location. It's HIGHLY recommended that it be checked and/or changed when the timing belt/waterpump/ belt tensioner is done. It's the same procedure and many shops DO drop the engine in order to replace it. Terrible design and yet one more reason I'm getting rid of mine. My back is getting worse as I get older and it's getting harder for me to work on cars.
     
  8. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    2,374
    The width of the 2.4L necessitates that the right side mount be placed inside the frame rail. The Neon SRT-4 (2.4L-turbo) is the same way.
    The PT is based on the Neon (PL) structure after all. The narrower 2.0L Neon engine has a conventional right side mount.
    I have replaced the mount without pulling the engine/trans out of the compartment, but it all has to be unfastened, supported and swung to the left in order to get the right mount replaced. Unless you have a chain hoist and lifting fixture at home or know someone who does, it may be best to let a shop do the job.
    Verify that the right mount is bad first.
     
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