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Thread: Strange Timing/Idle Problem

  1. #21


    I did make the -40°F adjustment, so it's above the -20°F setting as per your writeup, thanks for that by the way.

    I'm wondering if maybe I have things messed up because of the lack of throttle return spring. I'm tempted to try Chris's Idle Speed Adjustment Instructions from your (EFI System Pro) website, to see if maybe that will help.

    When I parked the truck yesterday evening and the idle was high, the IAC read 0% on the handheld. However, when I pulled the air cleaner off and put my thumb over the IAC port it had strong suction and covering it dropped the RPM down.

  2. #22
    Join Date
    Sep 2015
    Palm Bay, FL


    If your IAC is reading 0, but is letting air into the throttle body then you may have a bad IAC. I'd give Holley Tech a call on that one.
    Chris Myer
    800-880-0960 x654

    Check our website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  3. #23


    I think I may have figured out the trigger for my problem. It only does the high idle when I've been in the accelerator hard. If I just do "normal" accelerating for the entire commute, idle stays where it should.

  4. #24


    I'm also having the same problem. High idle after a drive & IAC at 0 (200 RPM+ higher). I lifted the air cleaner and covered the IAC hole and it leveled off. One other thing I noticed, is the longer I plugged off the IAC the more vacuum it applied to my finger.

  5. #25
    Join Date
    Dec 2009


    Quote Originally Posted by memphis View Post
    One other thing I noticed, is the longer I plugged off the IAC the more vacuum it applied to my finger.
    That's the IAC valve opening, trying to compensate for a lower idle than the target idle. Try opening the throttle blades a little more.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  6. #26


    Hi Danny, thanks for the reply. Yes I understand that, however, the idle is already too high with 0% IAC. In theory, I need to close the blades. I feel the IAC valve is losing its place as the vehicle is driven somehow, resulting in a theoretical 0% reading, however, it's open approximately 15-20%.

  7. #27


    What I see in my car is that the IAC has to close a lot more to keep idle down between a warm and a hot engine: At 180°F, I see 15% to 20% IAC opening, at 204°F only 5% to 10%. Maybe your engine is only getting to full temp when driving hard, and that's why the IAC can't compensate any more.

  8. #28


    I did think this too, but the amount of air coming in through the IAC hole while it's reading 0% cannot be accurate. If I key off/on again it returns to normal idle.

  9. #29


    Quote Originally Posted by memphis View Post
    ...If I key off/on again it returns to normal idle.
    It's a long shot, but double check your TPS is behaving normally and returning to zero. My idle & IAC went all screwy when my TPS went bad.

  10. #30


    My TPS reads 0 when idling (both prior to & after driving) and appears to be functioning correctly, but it's an idea.

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