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Thread: IAC issue maybe?

  1. #1

    Default IAC issue maybe?

    Hi all. SMPFI car has ran great idles well and over all happy with it. However, the other day, LOL, we all know the other day when crap happens. LOL. Anyway, my idle started not wanting to return to the 925 setting, it would stay high 1100 in D put her in P or N, and idle would shoot up to 2700. I thought darn, LOL. So I set throttle blades, and even after I closed them or crank them open, the idle is still screaming high 2k plus. Am I on the right path thinking it's the IAC motor?

  2. #2
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    It seems your TPS Position may not be consistently returning to 0%, and activating the IAC Hold Position.
    http://forums.holley.com/showthread....neral-IAC-Info (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

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    Danny thanks. What's weird is, all was well, car was great. But slowly I was noticing the idle getting higher and not returning normally, and this last high idle issue sorta cam on slowly. The idle is so high, I can drive 45 with foot off throttle, LOL. I had TPS Autoset correctly, I had IAC at 5 or so counts warm idle. I also looked at computer, and IAC was 38, TPS was 0 at closed throttle.

  4. #4
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    Quote Originally Posted by diehrd View Post
    I also looked at computer, and IAC was 38, TPS was 0 at closed throttle.
    Seems like your idle speed screw has back off, and the IAC was trying to compensate. Read this:
    http://forums.holley.com/showthread....neral-IAC-Info (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.

  5. #5

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    Danny, I can disconnect the IAC. Back off the idle screw all the way and the engine still idles at 1500 RPM. I can not get it below that. If I hook IAC back up it raises idle more. I have the IAC port plugged off, unplugged IAC, cycled key, started car. Engine idles 1500. Back idle screw all the way out, engine is at 1260 or there about. What could cause such a rise in idle speed?

  6. #6
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    The engine must be inhaling air from an additional source, other than the primary throttle blades.
    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.

  7. #7

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    I agree, I'm off to buy some starting fluid and check intake gaskets.

  8. #8
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    If you have a four barrel type throttle body, ensure the vacuum/air leak isn't coming from the secondary throttle blades (adjustment screw).
    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.

  9. #9

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    Quote Originally Posted by Danny Cabral View Post
    If you have a four barrel type throttle body, ensure the vacuum/air leak isn't coming from the secondary throttle blades (adjustment screw).
    I had a leak under the IAC motor bad. Changed gasket, same issue, bad leak sucking air like mad. Base plate under IAC was black, so was gasket. With new gasket, I'm idling at 1500 and it still has a small leak; same area as if I the surfaces are not true or flat.

    I pulled it again the the channel for air milled for the IAC motor sits almost off the edge of the mounting pad on the intake. Furthermore, I've used two different gaskets, have the same idle issue, but fit differently. 1) Covers the IAC port and the other does not. I'll get a photo, but basically the intake single plane mounting surface appears to prevent the IAC from letting air to enter the intake.

  10. #10
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    Connecticut
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    Some 4BBL type throttle bodies (LINK) need this "Throttle Body Base Plate & Gasket Set":
    https://www.holley.com/products/fuel...s/parts/508-17 (Holley 508-17 Throttle Body Base Plate & Gasket Set)
    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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