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Thread: GM IAC Stepper Motor Wiring

  1. #1

    Default GM IAC Stepper Motor Wiring

    Years ago when I bought my Holley system I was sold a GM style IAC. On this forum I was told the GM stepper IAC does not work as well as a Ford PWM. Because of that I lived with poor idle control. I just changed from gasoline to E100 ethanol and could not even drive the car. This caused me to pull the IAC and run some tests. The Holley harness is wired for a Mopar style IAC, but the Holley 543-34 is a GM style IAC. It is actually identical to a 1995 Corvette 5.7L IAC. This fits the Accufab Mustang throttle body. I re-pinned the Holley harness to match the GM pin layout and the IAC is flawless now. I have a really tight converter (high power turbo car) and my idle is 1300 RPM in gear or out of gear, and it never stalls. I'm putting this up because I spent hours maybe three years ago and again last Friday on this IAC issue. I had no idea the Holley EFI was pinned for a Mopar stepper wiring and the Holley IAC was a GM pin-out.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,674

    Default

    For reference: http://forums.holley.com/showthread....neral-IAC-Info (Scroll down to "IAC Motor Harness Connector PIN-OUTS".)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

  4. #4

    Default

    The pin-out thing needs to be in the manual. Just a simple one line statement like "Harness shipped with Mopar wiring", or "Needs repinned for GM IAC" would save multiple customers headaches. Even the people selling Holley kits have no idea what works, and neither did Holley tech support when I called them. This is the IAC I got from Holley, and this IAC is pinned like a Chevrolet.
    Click image for larger version. 

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  5. #5
    Join Date
    Nov 2014
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    Ont. Canada
    Posts
    1,380

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    Some Holley harnesses come pinned for a GM IAC, like the LS harness. Others, like the Universal harness come pinned for the Mopar IAC. Same thing happened to me, twice. In the beginning I used a different IAC and had to figure this out. And now I just finished making a new harness for the car. I moved the ECU to the trunk, and I'm going to put a LS in it. I used the LS wiring diagram, which uses the GM IAC, but I have the Mopar IAC. As soon as I connected it, I saw my mistake and had to re-pin the wires.

  6. #6

    Default

    I'm right in the middle of doing the same, Ford IAC to Holley 543-105. Is this a Chrysler or GM IAC? Has a flat style connector. Confusing for sure.
    '95 Lightning, HP EFI, 351W, S472SX-E, 20 PSI,N2O,pump & W/M

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,674

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    The Holley 543-105 is a Chrysler IAC motor. Please read the LINK in post #2.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8

    Default

    Just started mine tonight with the GM/Chrysler IAC. I agree with Tom, MUCH better than the Ford IAC. I also used the Accufab IAC adapter.
    '95 Lightning, HP EFI, 351W, S472SX-E, 20 PSI,N2O,pump & W/M

  9. #9

    Default

    I find the wiring issues with the GM/Chrysler units interesting as I may want to use the Holley output I'm using for the IAC for something else in the future.

    I'm currently using a Ford IAC and the idle is very solid, so this makes me wonder what the issue is with the Ford unit?

    Perhaps there's something I can do to induce the kind of issues you all are running into? I have a 250° duration @ 0.050" cam, 110° LSA, idling at 900 RPM N/A.

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