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Thread: Trouble adjusting the IAC on Sniper.

  1. #11

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    Quote Originally Posted by andyf View Post
    If the AC is erratic, then you probably have a vacuum leak somewhere. Do you have a PCV valve on the engine? If so, your PCV valve could be gunked up & sticky.
    Andy brings up a good point with the PCV question and vacuum. I didn't have a PCV system hooked up initially and my IAC was rock steady at 3% @ idle. After installing the PCV I had to adjust idle/IAC to compensate for the PCV (air/vacuum leak). A warm start now has my IAC moving up/down until vacuum in the crankcase builds & stabilizes which occurs in just a few seconds. Once it does then IAC is rock steady at 3%. My point is movement in IAC Position may be normal for a few seconds, but it should stabilize. If it doesn't then you have another source of air (vacuum leak) that you need to find.

  2. #12
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    Quote Originally Posted by travisch View Post
    A warm start now has my IAC moving up/down until vacuum in the crankcase builds & stabilizes which occurs in just a few seconds.
    Building a vacuum in the crankcase is not how to plumb for a PCV valve. There should be a filtered fresh air inlet on the other side of the engine. Gary
    Regards, Gary

  3. #13

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    If you have a big cam, the IAC will work a little harder as well.

  4. #14
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    Thanks for all of the input. I do not have a PCV system. I do have a brake booster that could be leaking I suppose. I may try removing the vacuum line from it and capping it to see if that helps. Does having the secondary throttle plates opening later make any difference?

  5. #15
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    Quote Originally Posted by Mazrolet View Post
    Does having the secondary throttle plates opening later make any difference?
    No, that's how a progressive secondary throttle linkage works.
    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/3000 RPM converter, FPP aluminum driveshaft, FPP 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 MT tires.

  6. #16
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    I know that. I was just meaning that when I adjusted my manual idle screw it only opens the primaries and the system is setup to normally open all 4. I just wondered if it confused the system at all.

  7. #17
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    No, the idle speed screw is only supposed to adjust the primary throttle shaft.
    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/3000 RPM converter, FPP aluminum driveshaft, FPP 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 MT tires.

  8. #18

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    Gary, I do have a breather on the other side, but I've blocked off most of the air holes leaving just a few for slight airflow, which results in a slight vacuum on the crankcase.

  9. #19
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    Quote Originally Posted by travisch View Post
    Gary, I do have a breather on the other side, but I've blocked off most of the air holes leaving just a few for slight airflow, which results in a slight vacuum on the crankcase.
    So now you create a vacuum at idle and very light load, but what happens to the crankcase pressure when you put your foot down? Blowby is now trying to push the oil and gaskets out of the engine, oil past the rear main seal, and at any weak point. The engine must have a large hose to the air filter assembly, or some form of vent for blowby. That's why you CANNOT plumb a restrictive PCV system like you have. Gary
    Regards, Gary

  10. #20

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    If you have that much blow-by then you have a problem, but a good topic for a different thread on a different forum vs hijacking this one.

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