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Thread: Idle Settings & IAC

  1. #1

    Default Idle Settings & IAC

    Hi. I've read quite a bit about the Sniper and IAC, but have a few questions:
    1) If IAC Position is reading 0% on the handheld, should it still be sucking air?
    2) I've adjusted the Throttle Blades to obtain +- 5% at hot idle, however, when "Cold", IAC will go to 100% - I take this as it is trying to maintain my target idle speed. It doesn't seem to quite get there. I take this as the throttle blades need to be open a little more?

    The engine is a 388 SBC, 224°/230° cam, aluminum heads, air-gap manifold. I've attached the Config File. I've flattened out CTS Enrichment & CTS Offset. I have the Target AFR based on highest vacuum reading obtained at hot idle. Thoughts? Todd
    Attached Files Attached Files
    Last edited by Wrenchhead67; 08-30-2019 at 01:42 AM.

  2. #2
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    Quote Originally Posted by Wrenchhead67 View Post
    1) If IAC Position is reading 0% on the handheld, should it still be sucking air?
    No. Maybe this is 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.

    2) I've adjusted the Throttle Blades to obtain +- 5% at hot idle, however, when "Cold", IAC will go to 100% - I take this as it is trying to maintain my target idle speed. It doesn't seem to quite get there. I take this as the throttle blades need to be open a little more?
    No, the idle speed screw/IAC Position % relationship is properly adjusted at hot idle.
    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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    I'll check wire routing and see what I can do. It does have an HEI distributor, probably a few inches between IAC motor & HEI. I'll check wiring, etc. Thanks Danny.

    Danny, if it's interference, what's being read on the handheld, may not be where the IAC actually is. So ±5%, could actually be more (or less). But given the IAC is still sucking air, I'd probably say it's open when the handheld (and ECU) think it's closed. So this would make sense that at 100%, I can't get to full target RPM. Thanks, Todd

  4. #4
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    Yep, it happened to me once with a fuel injector harness being too close to the IAC motor. Electrical interference freezes the IAC motor. At first, I didn't know why I couldn't lower the idle speed RPM.
    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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    This may or may not be related. At WOT, there's whistling and IAC Position shows 100% on handheld. As I understand it, IAC will not play a part in achieving Target A/F Ratio, so it should not be opening up for that reason. So, why would it open? At WOT, AFR is 12.5. If it were richer than that, wouldn’t the ECU pull fuel to try to hit Target A/F Ratio?

  6. #6
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    Quote Originally Posted by Wrenchhead67 View Post
    At WOT, there's whistling and IAC Position shows 100% on handheld. So, why would it open?
    Check your IAC Hold Position. It shouldn't be set to 100%. If so, change it to 20%. Also, ensure the TPS is functioning properly.
    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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    Thanks. IAC Hold is set at 20%. TPS seems to be functioning correctly. It reports what I think the pedal/throttle are at. I also checked all of the wiring. There’s about 2-3" between IAC & HEI. All plug wires, etc., are away from any harness wiring. Where they do cross, closest is about 2” and they cross at 90°, nothing runs parallel. Overall, there's probably more separation than on a new car.
    Last edited by Wrenchhead67; 08-31-2019 at 06:51 PM.

  8. #8

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    Here's a short datalog. This is a cold start (outside air about 80°F). IAC at 100%, does not hit the 1100 or 1050 RPM I have set for cold start. Config File posted in previous post.
    IAC drops to 20% when I open the throttle, like it should as IAC Parked is 20%. Thoughts?
    Attached Files Attached Files

  9. #9

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    Quote Originally Posted by Danny Cabral View Post
    Check your IAC Hold Position. It shouldn't be set to 100%. If so, change it to 20%. Also, ensure the TPS is functioning properly.
    So 20% is the preferred baseline or is this due to his engine combo? The manual states 30-40%. I'll try 20% in the morning.

  10. #10
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    Most applications have problems when the IAC Hold Position is too high. 20% should be fine.
    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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