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Thread: Cold Start Issue

  1. #51


    OK. Put new plugs in, same tune, still would not cold start without cracking the throttle. Once it did start, it kept running and idles pretty well. It does hot start well. Took it for a drive and it's running pretty well. However, the IAC% returns to zero at idle and no amount of adjustment on the idle screw will make it change.
    Last edited by Timbick; 07-20-2021 at 07:08 PM.

  2. #52


    When you go to crank it, do you turn the key to the accessory position then wait for the Fuel Prime shot before spinning it over? If not, maybe try that. If you're letting it prime and it still spins without firing, try adding to the Fuel Prime 10% at a time until it fires. Maybe even before that though, consider changing the IAC. Are you saying you can turn the idle screw out until the engine dies and the IAC will stay at 0%?
    '69 Camaro, 400 SBC, ProCharger D1SC
    1.302 60', 5.95@116.4 on pump gas.

  3. #53


    I do wait until the fuel pump stops before cranking (about 4-5 seconds) and I do have a solid 60 psi at the throttle body. I turned the screw out until the throttle arm stopped moving anymore, and it kept running with the IAC at 0%. While driving, it would go to 20% & stop, which is normal as I understand it.

  4. Default

    If the idle screw is all the way out and the IAC is still at 0%, that means the engine is getting air somewhere else, i.e. vacuum leak. While you're driving, the IAC will go to the IAC Hold Position set in the ECU. What's the IAC reading while idling with the car in gear?

  5. #55


    OK, I suspect that the vacuum leak is the TB to manifold. Either way, after tightening it down, I turned the idle screw in 1.5 turns since the last time I had it running it was backed all the way off. It fired up cold perfectly. I let it warm up and reset the IAC Position % at idle, went for a drive, had to tweak it again to stay steady at 4-5% and went for another short drive. This time it stabilized. When idling in gear, the IAC Position would climb to around 9% or so. It'll start well hot. I'm going to have to wait until tomorrow to check if it'll start cold.

  6. #56


    I just wanted to circle back to this thread and report where I'm at:
    IAC: After fixing an intermittent vacuum leak at the TB to manifold gasket, I was able to get the IAC to stabilize at around 4%. It continues to start hot well.

    Cold Start: I finally raised my Fuel Prime to 160% and this provides good cold starts.

    EMI/RFI: I reworked some of my wiring by placing the pink wires on a dedicated relay direct to battery (+) and better routing. I originally removed all of the unused wires from the 10-wire connector, but was waiting for cavity plugs to arrive while driving it. I also noticed that for some reason in one of the Config Files I've been using, the electric Fan #1 circuit had been activated in the Config File. I was getting interference at about the coolant temp which would trigger this fan (which I don't have). After plugging the cavities and turning off the fan control in the configuration, it hasn't had any interference issues since, knock on wood!

    I have driven it probably around 75 miles so far and the Learning function is working and it's running quite good. I noticed that when coasting down a hill, the IAC drops to zero, but rebounds to 4% when idling stopped. Is this normal? Thanks!

  7. #57
    Join Date
    Feb 2020
    Wheeling, WV


    Quote Originally Posted by Timbick View Post
    I noticed that when coasting down a hill, the IAC drops to zero, but rebounds to 4% when idling stopped. Is this normal? Thanks!
    Yes, that's normal. When the TPS is below 1% and you're within the idle RPM Ramp Down range, the ECU is trying to bring the engine RPM to the target idle RPM, thus under deceleration being driven by the drivetrain, the ECU will close the IAC port to zero.

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