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Thread: Issue with IAC?

  1. #1

    Default Issue with IAC?

    I noticed that I have a strange problem with the IAC. Here is a test I did: Water temp above 170°F, at idle (650 RPM), the IAC reads ~32%. I can adjust the idle screw 1/2 turn to open the throttle (IAC goes to 0%), then turn it back 1/2 turn in the opposite direction to close the throttle and the IAC will read 4-6%. I shut off car, restart and the IAC is back to ~32%.

    I'm testing because my engine will occasionally die coming down to idle and then be a little difficult to start. FYI: It's a stock LQ4. I have done the above a few times with the same results. Can you give me some ideas on what may be the issue? Thanks for any advice. Robert

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,909

    Default

    Ensure the TPS Position returns to 0% at idle, and try lowering the IAC Hold Position.

    Typical IAC Control/Ramp Down Parameter Settings
    Advanced Idle Control: ......................... Slow (Usually the best control.) Sniper EFI users select "Sniper TBI".
    IAC Type: .......................................... Stepper (4-wire), PWM (2-wire)
    IAC Hold Position: ................................ 10%-30%
    Ramp Decay Time: ............................... 1.0-3.0 sec
    RPM Above Idle To Start Ramp: .............. 1000 RPM (Or higher.)
    RPM Above Idle To Re-enable Idle Control: 50-200 RPM (This setting can be finicky.)
    Not IAC, but Idle Spark control usually works well at: 30-40 P Term & 50-60 D Term.
    http://forums.holley.com/showthread....neral-IAC-Info (General IAC Information - Read "IAC NOTES")
    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
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,424

    Default

    Are you using the Idle Spark control? If so, this will also affect your idle speed and change the IAC Position.

  4. #4

    Default

    No, I'm not using spark control. But I do have a successful update. I went through the IAC Position adjustment like described in the manual, instead of immediately turning off the engine and restarting. I made a 1% change to the IAC Hold Position and saved the Config File. When I started backup, the IAC stayed where I had set it, ~8%. It makes no sense to me, but it seems I needed to save the Config File before I cycled the engine. After that was set, I used Danny's typical settings to get it to idle a little better. Thanks for the info!

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,909

    Default

    Quote Originally Posted by Cunning69 View Post
    After that was set, I used Danny's typical settings to get it to idle a little better. Thanks for the info!
    You're welcome.
    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.

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