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Thread: IAC going crazy, warm idle.

  1. #1
    Join Date
    Aug 2019

    Default IAC going crazy, warm idle.

    The IAC starts by blipping to around 50% really quickly then back to normal. Then as it sits & idles it gets worse & worse until the engine dies. I included a datalog, the end part is it sitting idling with the issue. I did hold my finger over IAC port for a minute in that datalog and it idles fine just a little low. I called Holley Tech on Friday. They suggested RFI and to move my coil away from IAC. I did that and it didn't change. I looked down the IAC port while it was doing this and the pintle was going in & out really fast like the datalog 1 shows.

    I updated the firmware and started over this morning. Started let warmup and it started to Learn, once it looked there I tried idle in gear, everything was fine there too. I moved the throttle a little bit and everything seemed okay. I went and closed hood to take for a drive and I heard it doing the same thing. It ran for about a minute after that and eventually died. This is datalog 2. Here are some engine bay pictures so you can see my routing and let me know if something looks bad.
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    Last edited by gearhead927; 08-21-2019 at 10:42 AM.

  2. #2


    If your IAC is going crazy and making the engine run funny it's most likely RFI. What they didn't tell you, shame on them and shame on me for not posting sooner, is to remove every wire from the system that you're not using to run the car. You have a lot of sources under the hood that create electrical "noise" and it messes with the EFI system. If you have any loose wires, especially the ignition timing wires, they'll act as an antenna and pickup that unwanted noise.

    I had this same issue a year ago. I went round & round with Holley; they kept saying I did the setup wrong. After finding one guy who actually knew what he was doing, we were able to agree it was RFI. Removing the wires fixed the issue and it's run perfect ever since. Also just checked, they did add a little blurb on page 20 of the manual for "unused wires".

  3. #3


    Gearhead, where are the main power & ground for the Sniper connected? I don't see them connected to the battery in the picture, but it's hard to tell. Looks like you have some grounding issues.
    Last edited by gregs69rs; 08-29-2019 at 09:47 PM.
    69 Camaro
    400 SBC, ProCharger D1SC

  4. #4
    Join Date
    Dec 2009


    An improperly functioning IAC motor can also be an electrical interference issue. Ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring. The IAC motor is easily susceptible to this.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" Dart SBF, 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.

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