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Thread: High deceleration to idle RPM with Sniper 92mm throttle body.

  1. #1

    Lightbulb High deceleration to idle RPM with Sniper 92mm throttle body.

    Hi all. Owner of a 2002 Camaro 5.7L engine (LS1) contacted me as they had a CAM, FAST intake, headers, larger fuel injectors and a Holley 92mm Sniper EFI throttle body installed by a shop about one year ago. Ever since this was done the engine would barely run and he has gone to three other shops and could not find the problems. He contact me as I do custom PCM tuning for GM vehicles, I am not local to him. The tune that was done was crap and by having Camaro owner use a OBD-II scanner on a laptop that records, and emailed to me the recordings I was able to point him to intake, exhaust leaks, and believe it or not the fuel injectors.

    On right head (BS) were missing the bottom O-rings.

    I have cleaned the tune, up but one problem still exists and that's on deceleration (lifting on gas pedal)
    the RPM will not go below about 2,000 RPM even though tune sets it to 850 RPM for idle.

    Only when car comes to complete stop does RPM finally come down.

    Cylinders are stock, no stroke or bored.

    Original stock would be 75 mm MAF and same size for throttle body,
    but now using a FAST intake manifold, 90 mm MAF and this Holley 92 mm Sniper TB PART# 860004-1.

    Questions:
    1) Is this TB just wrong for stock cylinder volume?
    2) Any known faults with this model Holley TB?
    3) Possible the IAC, it's wiring or Holley TPS sensor not workable for GM PCM?
    4) Springs or linkage to cable of gas pedal not right for Camaro.
    5) Stock Camaro wiring pin-out wrong for the Holley IAC.
    6) Bit odd is using OBD-II scanner TPS at times reports at idle at 0% angle and sometimes 7%.

    Makes no difference if cold or hot startup or Open/Closed Loop, anytime gas pedal is lifted for deceleration.
    the RPM just do not come down, even if for a test lowering timing in tune, same results.
    Thanks for any ideas you have! JR

  2. #2
    Join Date
    Dec 2009
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    Quote Originally Posted by teamzr1 View Post
    I have cleaned the tune, up but one problem still exists and that's on deceleration (lifting on gas pedal)
    the RPM will not go below about 2,000 RPM even though tune sets it to 850 RPM for idle.
    Determine where the engine is inhaling the extra air. Vacuum leak (check for leaks), defective IAC valve (temporarily block off IAC air inlet port), or throttle body blade not returning to idle position (momentarily block off throttle body with your hand during deceleration).

    (Please don't type your posts like you're texting. It takes me a long time to edit it. At least use Spell Check before posting.)
    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, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 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.

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