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Thread: High Idle Problem

  1. #1

    Default High Idle Problem

    Hi, I'm new here. I'm having an issue with Atomic EFI high idle. It's installed on an engine I built for a truck. I'm in the process of building, so it hasn't been on the street yet. When I first installed the system it worked just fine. Now, the idle won't drop below about 1100 RPM. With key on only IAC count varies widely. When engine is started it goes immediately to zero. I currently have the throttle blades closed all the way, but engine still idles at 1100. Maybe IAC is stuck open? Dirty? Like I said, it used to idle fine, target idle is 600 with manual transmission. It seems to me if blades are closed all the way and IAC count is zero then it shouldn't run at all (not enough air, correct?) Adjusting blades while running doesn't change IAC count, always at zero. I have double checked timing and re-zeroed the pointer (it was off). As of now I'm assuming the IAC is faulty. Timing control is disabled, I'm using a distributor from Progressive Ignition. Any advice to get me back on track would be appreciated! Thanks, Dave.

    1965 Ford F250
    FE 445 cu. in.
    Comp Cams 218°/224° @ .050" lift.
    Edelbrock Performer dual-plane with 1" open spacer.
    Edelbrock Performer RPM heads.
    Manual transmission.

  2. #2

    Default

    The IAC count at zero, means the ECU has fully closed the IAC trying to achieve the target idle. The intake is possibly getting air from somewhere. Verify there are no vacuum leaks such as the throttle body gasket, intake manifold gaskets, PCV, and the power brake booster. What's the MAP sensor reading at idle?

  3. #3

    Default

    Thank you. The first thing I did was look for vacuum leaks, but I'll check again. I didn't look at the MAP reading since it won't idle anyway, but I'll look at it. I forgot when I was adjusting the timing, I did have a pretty good backfire that may have damaged the IAC too. Is there a range that the MAP reading should fall into? Dave
    EDIT: I checked the MAP reading, it's 13-14 kPa.

  4. #4

    Default

    If the IAC is stuck open, you can block the IAC air inlet ports with duct tape, and see if the idle speed drops. If no change, keep looking for a vacuum leak. Also verify the throttle linkage isn't being held open. The TPS should be at 0%. To test the IAC, measure the resistance of the two coils between pins A-B & C-D.

  5. #5

    Default

    I fixed the idle issue. The IAC was in fact faulty. I replaced it with a new one and all is fine now. Thanks for your help.

  6. #6

    Default

    Glad the problem has been solved. Thanks for the update.

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