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Thread: How to adjust for decel after installing new IAC valve?

  1. #1
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    Default How to adjust for decel after installing new IAC valve?

    Hello, I just plugged in a new IAC and followed instructions to get it adjusted. Sitting at about 9%. It's a 396ci LT1, with a turbo, solid roller engine with a healthy camshaft. When I come to stop at a light or stop sign, when I push the clutch in as it comes off of idle, it stalls out. Not sure where or how to correct the settings for deceleration. Any help is greatly appreciated.
    Last edited by 8SEC6SPD; 07-11-2018 at 09:09 AM.

  2. #2
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    Read 8th paragraph: http://forums.holley.com/showthread....2523#post62523 (Holley EFI Tuning Tips & Information)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3
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    Danny, thanks for the direction!!!

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    You're welcome.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5
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    I did a whole bunch of reading, thanks so much for the links. IAC is at roughly 9-10% with hot engine now.

    I figured it couldn't hurt to post these settings up. This initial tune was done on the dyno and setup by Scott Clark in a recent EFI class he held. Made a tick under 700 at 5.6 psi. It made over 1000 @ 1x psi, with plenty of room to grow.

    It's an '96 Chevy Camaro LT1 with a turbo, and it has a T56 behind it. It has a fairly aggressive solid roller cam in it.

    I think I need to increase the "RPM Above Idle To Start Ramp". Question is, if I have my hot idle is at 1075 RPM, how much higher would be a good place to start for setting this? Do you see anything else out of the ordinary? Also, what you see was prior to me installing new IAC valve. Thank you. Taner
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    Last edited by 8SEC6SPD; 07-11-2018 at 09:14 AM.

  6. #6

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    So hot idle is 9% and IAC Hold is 10%? I would go with a larger spread. Heck, IAC idle "should" be 2-5% at hot idle, not in gear. Then load it up with as many accessory loads as you can (in gear, power steering, brakes, air conditioning) and watch what IAC goes to. Add 5 or 10 to that number, and you have your new IAC Hold.

    The other issue I've seen time & time again is too much timing at idle. This results in not enough air. This will cause stalling coming to a stop or even just slamming the throttle shut. Or like you described, takeoff is poor. Especially apparent in a stick car.
    Typically you want your Idle Spark control to bounce 2° or maybe 3° each side of your idle setting. If it's bouncing wildly or constantly above your commanded spark, you don't have enough air.

    If you want to send me the GF I can have a look, and maybe do some IEA tuning. See my thread in the HP section.
    EDIT: So it's definitely the IAC Hold isn't high enough, but let's redo everything to make sure it's right.
    Last edited by allan5oh; 07-11-2018 at 03:33 PM.

  7. #7
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    Stalling issue is not when I accelerate, it's only when I depress the clutch is when it wants to stall. It 2-5 is better then I can make it so. Thanks! I'll start there an see if that makes any improvement.

  8. #8

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    Quote Originally Posted by allan5oh View Post
    The other issue I've seen time & time again is too much timing at idle. This results in not enough air. This will cause stalling coming to a stop or even just slamming the throttle shut. Or like you described, takeoff is poor. Especially apparent in a stick car.
    What do you think the timing at idle should be?

  9. #9

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    Not sure, don't know those engines, only SBFs. But I've had a few guys have excellent luck with lowering timing and increasing air on LS engines. Andrewb had the exact same problem and it was solved with the above. Engine would stall when clutch pedal pushed coming to a stop. He fixed that and noticed a few other things improved. If lowering timing/more air isn't a good option because of the cam, maybe more idle RPM is in order. Wouldn't hurt to post the Global File either.
    Last edited by allan5oh; 07-11-2018 at 11:18 PM.

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