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Thread: IAC Fluctuating Between Starts

  1. #1

    Default IAC Fluctuating Between Starts

    Setup: '66 Mustang, Ford 289, Cam: 0.050 @ 282° duration. Sniper install kit with negative coil timing control.

    Issue: I had the setup on the car and had it running good for the past few months. One morning I went out and noticed the car was starting hard, but finally got it going and warmed up. When I looked at the handheld the IAC was showing 35-42% at hot idle, when it had previously been in the normal 5-10%. Removed the air filter and noticed that no air was passing through the IAC so figured it was defective. Replaced it, and now have the airflow through the IAC opening.

    The issue I face now is that I can get my hot idle IAC down to 5-10%, but when I turn the car off to TPMS reset, when I restart the car it jumps back up to around 25-30% and holds. I can adjust the idle up to around 1100 RPM, then back down to the target of 800 and it will bring it back down to 5%. Anyone have any ideas on what could be causing this? I have checked the engine for vacuum leaks and found none.

    I have two datalogs, one from when it was running, and the second after I restart it and show how the IAC increases again and can adjust the idle speed to correct it. Maybe a fresh set of eyes on the GCF might catch something I missed?

    GFC: https://www.dropbox.com/s/ilq5unz96b...am.sniper?dl=0
    First Start: https://www.dropbox.com/s/w06zavoje5..._Start.dl?dl=0
    Second Start: https://www.dropbox.com/s/lqsternrhg..._Start.dl?dl=0

  2. #2
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,418

    Default

    Raise your "RPM Above Idle To Re-Enable Idle Control". It's at 100 right now. Raise it to 300 to 400.

  3. #3

    Default

    I tried setting it to both 300, 350, 400. Problem still persists. I have also noted that if I rev the car and let off, it will lean out to 17-20 AFR.

  4. #4
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,418

    Default

    Try using a lower IAC Hold Position.

  5. #5

    Default

    I tried lowering it with no change. I don't get why the IAC loves 30% so much.

  6. #6

    Default

    Was there a solution found? I have a very similar issue, and would love to know how you solved this problem. Thanks!

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