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Thread: Bad IAC valve?

  1. #1

    Default Bad IAC valve?

    After doing some work on the truck recently that affected idle and tuning, I started having trouble with getting idle RPM dialed back in. Might have had an idle RPM issue before, hadn't driven it much in a bit and wasn't paying much attention to IAC % or RPM when I did. After chasing the problem for a bit I noticed that the IAC didn't see to be working right.

    I've read that when the Sniper is turned on one of the first things that happens is that the IAC cycles then return to Parked Position for engine temperature. So when ignition switch is turned on, the IAC motor should move. Am I understanding this correct?

    When the key is turned on my IAC does nothing. I didn't hear it so I grabbed a flashlight and watched it while dad switched on the truck. It didn't budge. So am I correct in thinking that I might have a bad IAC valve?

  2. #2

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    Could be. One easy check is to watch the handheld to see what the IAC is doing when the engine is running. The IAC should follow the programming instructions. You can also change the idle speed and see if the IAC moves to control the idle speed.

  3. #3

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    Well it's hard to describe. I've successfully set idle a few times before using Holley's instructions and Chris Myer's instructions. I think I know what I'm doing there. With engine at operating temperature, if I dial in idle speed using throttle stop the IAC sits at 0% like it should do. If I budge the throttle screw back out to decrease RPM so I can set the 2-8% IAC, it's impossible to hit the desired percentage. Just barely decreasing RPM with screw the IAC will climb all the way to 100% without having any effect on engine RPM. When I say barely decrease, I mean idle is set to 750 in handheld, I just drop it down to 700-725 with the throttle screw, the IAC will climb to 100% trying to increase RPM but have no effect on RPM.

    Did not try to watch IAC valve while engine was running. Only way to do that in this vehicle is lean directly over a spinning fan and that's not going to happen.

  4. #4
    Join Date
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    Ont. Canada
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    When the IAC says 100%, put your finger over the IAC air inlet at the top of the throttle body. Is it pulling air? It should be. Check it at 0% & 100%.

  5. #5

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    When the IACs are bad they'll show they're functioning on the screen when in reality they aren't functioning properly. I've had two Snipers with bad IACs right out the box. Go to your local parts store or Chrysler and get a new one if you want to quickly change it out and see what happens. Never hurts to have a spare with you anyways. Think of it like carrying a ballast resistor in the glove box of your old Mopar all the time.

    Chrysler PN# 53032067AB or 53030657AD will work. Your local parts store can use those numbers to cross reference for you if you don't want to buy from Chrylser.

  6. #6
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    Quote Originally Posted by Moparmatty View Post
    When the IACs are bad they'll show they're functioning on the screen when in reality they aren't functioning properly.
    That's correct, even when they freeze due to electrical interference (not a defective IAC motor).
    Ensure the fuel injectors or 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 electrical interference, and it'll cause strange occurrences and become inoperable.
    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.

  7. #7

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    Yep, it was a bad valve. Moparmatty thanks for the part numbers. The first one wasn't available locally on short notice. I'd read a snippet or two online saying the second application would work as well, but good to see it here as well. Seems the only difference is the angle at which the plug is clocked, plenty of slack in the wire to connect it. Stuck new valve in and works perfectly, old valve seems to have been stuck fully extended.

    Danny thanks for the recommendation. Part of the recent work was swapping over to the Dual Sync Distributor with HyperSpark coil and CDI box. Had to make up new plug wires, so made sure they were routed in such a way as to be unlikely to cause interference, and they're no where close to the IAC motor and wiring.

    Now to figure out how to get back starting the way it used to. Before the ignition upgrade, when the key was turned it fired right up. Now it's got to crank over for a bit before it fires and runs. I tried to copy old timing parameters as much as possible, but I think it's still off. Suspect I need to play with Cranking Timing and maybe Crank To Run RPM a bit. I'll start a new thread if I don't get that figured out shortly.

  8. #8
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    Quote Originally Posted by JoshT View Post
    Suspect I need to play with Cranking Timing and maybe Crank To Run RPM a bit.
    I doubt it. Just set those two parameters to what they were before (when it started well).
    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.

  9. #9

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    I hate using this forum on my cellphone. Typed this reply once, tried to edit it and the site thought I clicked delete. I clicked on the message to edit it, not delete damned it. Rant over...

    As I said above "I tried to copy old timing parameters as much as possible". I got idle, cruise & WOT timing, but Cranking Timing was the one I couldn't get. On Ford Duraspark II system the Cranking Timing isn't base timing as suggested by some places (EFISyetemPro.com), but instead is a timing retard built into the Duraspark module which I've read to be about 6°. In hindsight I probably could have gotten it with a bit of wiring trickery, but didn't think about that until after it was removed. Not going to reinstall now just for that.

    Since I didn't get the Cranking Timing I'm starting at idle timing (12°) and working back to find where it best cranks and starts. Currently set at 11.2° any higher and it starts kicking back, going lower doesn't seem to make an improvement. At all settings it takes cranking over for a bit before it starts and runs, before with the Duraspark II it started right up as soon as I hit the key. Once it starts it runs fine, just takes longer getting it to start.

    EDIT: Of course I'm also looking at your reply in "Hard time tuning cold start idle." Wandering if The Cranking Fuel (lb/hr) & IAC Parked Position might need to be adjusted instead. I'll do the little test you mentioned in the link next time I'm at the truck.
    Last edited by JoshT; 12-01-2019 at 01:52 PM.

  10. #10
    Join Date
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    Is the Holley dual sync distributor looking for the cam signal before it will let the engine start?

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