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Thread: IAC Constantly Flowing

  1. #1
    Join Date
    May 2018
    Dublin, OH

    Question IAC Constantly Flowing

    Hello, this is my second thread about my IAC problem, but since I have not received any information that has helped me, I decided to do more testing and create another thread. My IAC valve is always letting air in through its holder thing. When I plug in the laptop, turn to car to run, then change the IAC Park Position in my temperature range, it moves. I changed it to 100% and the cone moved upwards, towards the top of its holder, and when I set it to zero it moves down towards the bottom of its holder and the bottom of the throttle body.

    1991 Mustang, 347 stroker SBF with HP EFI
    Could this be a problem with the wiring of the IAC connector?
    I am using an IAC valve from a 1994 Z28 Camaro, and a FAST holder to bolt it to the throttle body.
    I believe I may have already swapped two wires when I was first building the engine, but I can't remember exactly.
    The only way to keep it starting and running while cold (45-70°F) is to give it .5%-2% throttle.
    Is there any other way to test this? Thanks.

  2. #2


    Check your pin out at the IAC plug AND ECU plug via the Holley wiring diagrams. I recently had an issue where no matter what I did I could not get the IAC to close completely even though the count showed zero. Turns out the plug at the IAC was mis-pinned at the factory. Once you have made darn sure it's correct set the IAC to GM LSx in the idle ICF table then try it. After that if you still need to add a tiny amount of throttle, you'll need to start increasing the IAC Park Position a little at a time until you find the sweet spot I go in steps of 10.

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