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Replacing IAC--does it need training?

Discussion in 'FAST Support Forum' started by daddytoy, May 1, 2018.

  1. daddytoy

    daddytoy Member

    Joined:
    Dec 10, 2011
    So the IAC just quit on my SBC engine running XFI. Cold(ish) start, idle speed coming down per the idle speed vs CTS trace and then it just popped up to a high idle speed--near 2000 rpm. I found that the IAC motor was wide open and not responding to the XFI which was commanding 0 counts.

    I'm using an Accel TB with a TPI style screw-in IAC (like this--http://www.fuelairspark.com/fas/iac-gm-tpi-stylehtml/). How do I check the four wires to verify that the XFI is putting out? I see IAC Output A & B, High and Low on the schematic, but not sure what values should be across each of the High and Low.

    Assuming the XFI is operating correctly and it's just the IAC motor, when I screw the new one in, does the system somehow need to be trained to determine the closed vs open position like the TPS?

    Any advice will be appreciated.


    THANKS in advance.
     
  2. 33Dan33

    33Dan33 New Member

    Joined:
    Jan 8, 2015
    I had an IAC go bad last summer, and my XFI 2.0 didn't set any codes. I believe what happened is that things got a little too warm under the hood of my car on a hot day and my idle speed suddenly dropped well below where it normally runs. The engine also became hard to start when it was cold, and wouldn't idle well at all. Instinct told me to replace the IAC, and when I did the engine went right back to operating normally or within the parameters I have set. So to answer your question, no you shouldn't have to train a new IAC. And if you screw a new one in and still have the same problem, it might not hurt to have a spare in case you ever need one. I have a spare in case the same thing ever happens to me again..
     
  3. daddytoy

    daddytoy Member

    Joined:
    Dec 10, 2011
    Thanks, 33Dan33.

    Does anyone have advice on how to test the output from the XFI just to verify it's the IAC motor and not the XFI itself?

    THANKS
     
  4. daddytoy

    daddytoy Member

    Joined:
    Dec 10, 2011
    Well, I got antsy and picked up a new IAC Motor. No change. Still doesn't respond to commands from the XFI box.

    Any suggestions to ring out the connector to see if any signals are being sent?
     
  5. Dart67

    Dart67 Member

    Joined:
    Sep 12, 2011
    Location:
    Jessieville, Arkansas
    Did you unplug the IAC with the engine running ? If so, you more then likely knocked the IAC drivers in the ECU out and it will have to be sent in for repair.

    Don't ask me how I know that !!!!!

    Herb
     
  6. daddytoy

    daddytoy Member

    Joined:
    Dec 10, 2011
    Hey, Herb. No, I didn't unplug the IAC with the engine running. It just quit.

    I ended up having to send the ECU to FAST and they replaced the whole board at no charge because they said there were some manufacturing issues they didn't like. On a 7-yr-old build. Really fantastic guys at FAST. Plugged it back in and it fired right up with a fully-functioning IAC!
     

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