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Thread: High idle

  1. #1
    Hybrid booster
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    High idle

    Car is a 91 Spirit RT. All stock except for a cold air intake and oil catch can. Car will idle fine at start up, but when slowing down and stopping in traffic the idle hangs at 1400 rpm or so. Idle at start up is 800 to 1000 rpm. I've checked for vacuum leaks and found nothing. The IAC was replaced at one point because I went through some water and it splashed up into the engine bay. At that point the idle was fluctuating really up and down but a new IAC did the trick. I also put in a new throttle body gasket when I had the throttle body off to replace the IAC. The car runs fine other than the high idle, and I'm getting ready to put it away for the winter. Any insight is appreciated.

  2. #2
    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: High idle

    Is your speed sensor reporting the correct speed in the OBD scanner?

  3. #3
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    Re: High idle

    Quote Originally Posted by tryingbe View Post
    Is your speed sensor reporting the correct speed in the OBD scanner?
    Just actually picked up a scanner this week and haven't tried it out yet.

  4. #4
    Supporting Member II Turbo Mopar Contributor rgl10's Avatar
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    Re: High idle

    Hopefully your scanner will have live data. Watch the IAC counts when coming to a stop. If they drop to zero then the computer is trying to slow down the idle but the engine is getting air somewhere else so its probably a vacuum leak of some sort. If its up over more than 10 to 20 steps then the computer is holding it up there. Low refrigerant that causes the ac clutch to cycle really fast can cause a fast idle when the ac or defroster is on. Hopefully the iac or ais whatever you want to call it is the correct one for that car. There are different pintle sizes on some of those. It does not have a custom calibration in the computer does it?

  5. #5
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: High idle

    Whenever I have a high idle under those conditions, I know it's time to get the carb cleaner out and thoroughly clean the TB especially the IAC portion.

  6. #6
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    Re: High idle

    Quote Originally Posted by rgl10 View Post
    Hopefully your scanner will have live data. Watch the IAC counts when coming to a stop. If they drop to zero then the computer is trying to slow down the idle but the engine is getting air somewhere else so its probably a vacuum leak of some sort. If its up over more than 10 to 20 steps then the computer is holding it up there. Low refrigerant that causes the ac clutch to cycle really fast can cause a fast idle when the ac or defroster is on. Hopefully the iac or ais whatever you want to call it is the correct one for that car. There are different pintle sizes on some of those. It does not have a custom calibration in the computer does it?
    The calibration is stock and the IAC was replaced with a correct replacement about 2 years ago.

  7. #7
    Supporting Member II Turbo Mopar Contributor
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    Re: High idle

    Quote Originally Posted by cordes View Post
    Whenever I have a high idle under those conditions, I know it's time to get the carb cleaner out and thoroughly clean the TB especially the IAC portion.
    Absolutely!! I need to do this 2-3 times per year as my car is a DD and I have the old style AIS.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  8. #8
    boostaholic
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    Re: High idle

    Quote Originally Posted by tryingbe View Post
    Is your speed sensor reporting the correct speed in the OBD scanner?
    I second this, any time my speed sensor starts acting up, my idle coming to a stop goes all out of wack.

  9. #9
    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: High idle

    Quote Originally Posted by DoubleD View Post
    I second this, any time my speed sensor starts acting up, my idle coming to a stop goes all out of wack.
    I gone though three 2 wire sensors before I converted to a 3 wire sensor, no issue yet.


  10. #10
    Supporting Member II Turbo Mopar Contributor Dr. Johny Dodge's Avatar
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    Re: High idle

    idle speed motor issues that won't go away with new ais installation..

    had this issue with my TII converted 86 TZ
    used an 88 harness so I didn't have an ais wiring conversion to deal with

    so anyway , car ran like poo
    threw code for AIS
    okdoky , install new AIS .. no fix , same problem remains

    so, scratching my head I asked myself what's the closest thing to the AIS that could be causing an idle speed issue?

    turned out it was one of those close to genius moments

    throttle position sensor...don't get any closer than that..

    I pulled one of the other car next to mine and sure enough all the issue was solved .. instantly

    I swapped the old ais back on
    problem came back

    swapped the new ais back on , swapped old tps back in
    problem came back again

    so.. it wanted BOTH the AIS and TPS but never bothered to tell me about the TPS

    it was then I figured also my car must be a girl car ....

    (different issue, -stalling at a stop can also be caused by a leaking brake booster)

  11. #11
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    Re: High idle

    Had to do some work on my daily driver today so tried using the Spirit for some running around. Now it's idling at 1800 to 2000 rpm. Think it's time to put it in the garage for the winter...

  12. #12
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    Re: High idle

    Changed out the speed sensor today. No help, idle even seems more erratic. Gotta get to the throttle body and IAC I guess

  13. #13
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    Re: High idle

    sounds like it bud. time to clean it out.

  14. #14
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Re: High idle

    My Daytona does the exact same thing, but only when the defrost is on . . . which is supposed to raise the idle to account for turning the AC pump, but that's currently disconnected due to a bad clutch.

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