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Thread: IAC uncontrolled at 65% & 2000 RPM.

  1. #1

    Default IAC uncontrolled at 65% & 2000 RPM.

    I have a fairly new install on a Chevy 383. Had a TPS sensor fail, replaced it, running great. The one issue I'm having is every once and while, when the engine is warm, I will get an uncontrolled IAC @ about 65%! It brings my idle up to 1,800 - 2,000 RPM. Blipping the throttle does nothing. The only thing I found that helped once, was lightly tapping the throttle over & over, and every tap brought it a little lower, until it finally went back to idle control around 6-9%.

    Things I did notice. Sometimes the electric fan was running, sometimes it happens when engine gets loaded at idle like turning the steering, and electric fan on. I'm thinking maybe electronic noise freaking it out, but the fan control is on the other side of the engine bay with no wiring near it, and I can’t duplicate the issue. Also thinking maybe with the distributor & plug wires close, an interference there, again, very random though. Anyone have a similar crazy high IAC? Also, my IAC Parked Position for IAC is only 18%, or close to it. I have a datalog from the occurrence.
    Click image for larger version. 

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  2. #2
    Join Date
    Dec 2009
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    Connecticut
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    18,629

    Default

    Check the things in this thread: https://forums.holley.com/showthread...-Idle-Solution! (Holley Sniper EFI High Idle Thread)
    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

    Default

    I have read that before, but don’t believe mine is set low at the -40°F location. I will double check tonight, but don’t think that’s it.

  4. #4

    Default

    Check to make sure your rear throttle blades are closing. I had a similar issue, wound up my rear throttle blades would not close all the way all the time.

    I loosened the butterfly plate screws, held the shaft closed all the way and retightened the screws, aligning the plates in the bore. I then added another turn/wrap on the spring on the rear throttle blade shaft. This fixed my issue of the blades staying open some on occasion, usually when the engine was hot.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  5. #5

    Default

    I saw that same idea on another post, may have been your reply to someone else. I took a look at that yesterday and put a small amount of oil on the linkages to be sure they were smooth and everything seemed to be OK. To verify that that wasn’t it, I opened the rear blades by hand, while the engine was running and watched the handheld. Had increase of RPM obviously, no TPS as expected, and no change in IAC either. I thought for sure that was going to be it until I saw that it didn’t change the IAC percentage like what I was seeing when it was giving me the uncommanded situation. Do you think those being stuck open could cause IAC to increase?

  6. #6

    Default

    Not sure. The way I found my issue was when the RPM was up, I reached in and was able to close the rear blades a little more, and the RPM dropped back down to where it was supposed to be.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

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