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Thread: High idle issue

  1. #1

    Default High idle issue

    Hello all. Just wanted to see if I was missing something in my investigation into my 88 T-bird 2.3T idling >1300 rpm.

    So far I've checked the Vane Air Flow (MM volt test), Vane Air Temp (MM resistance test) , ECT Sensor (MM VOLT/Resistance) , ACT (MM VOLT/Resistance) , EVR (you get the point), BMAP, TPS, ISC-BPA, HEGO.

    When I unplug the ISC/IAC the idle gets lower. That's why I checked all sensors I thought could be effected. Seemed more computer driven than a vacuum leak.

    Any ideas moving forward?

    Appreciate the help

    Sent from my iPhone using Tapatalk
    Last edited by cafournet; 07-12-2019 at 12:09 AM.

  2. #2
    FEP Super Member JTurbo's Avatar
    Join Date
    Jan 2006
    Western MA


    High idle is generally caused by a faulty TPS / Throttle Position Sensor.

    To check the TPS, you need an analog volt meter. Connect to the wire that feeds the PCM. With the car off, but key on, you should be able to verify that the voltage increases from ~1V at closed throttle to close to 5VDC at wide open throttle. There should be no "glitches" in the voltage as you open the throttle blade from idle to wide open.

    A lot of times there is a "bad spot" in the variable resistor within the TPS and when the PCM sees a voltage spike or drop out, it just ignores the sensor and arbitrarily increase the idle to >1k RPM's.....

    Good luck!
    1979 Indy Pace Car Mustang 302 / 5spd
    1982 Mustang GT T-Top 302 / 4spd
    1986 SVO Mustang - 1C

  3. #3
    FEP Super Member gr79's Avatar
    Join Date
    Jun 2009
    SE Michigan


    Had an intermittent 2000 rpm high idle when driving, Ranger 2.3, in 2007 and 2011.
    Slowing down or when changing gears. 'Kicking' the pedal like a carb high idle had no effect.
    Lightly tapping the IAC would get the idle down.
    Removed and cleaned it. Ok since.

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