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Thread: Idle Settings & IAC

  1. #11

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    OK, but if IAC is at 100%, I assume it's trying to smooth idle and get to cold idle RPM of 1100 at that temp. I'm thinking this means:
    Throttle plates are too closed and IAC can't reach target RPM.
    Or
    IAC reported position is wrong. Thoughts?

  2. #12
    Join Date
    Dec 2009
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    Quote Originally Posted by Wrenchhead67 View Post
    Throttle plates are too closed and IAC can't reach target RPM.
    Yes, ensure the idle speed screw/IAC Position % relationship is properly adjusted at hot idle. If so, you may have a vacuum leak at hot temperatures that's causing you to close the throttle blades at hot idle. A cold engine shouldn't need 100% IAC Position.
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  3. #13

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    Thanks. I’ll check for vacuum leaks - did not have any with the old carb. I can also block off the PCV hose while troubleshooting, since by design, it's sorta like a vacuum leak. :-) I have fuel/temp enrichment pretty flat above 60°F. Not too many days below that when I'm driving it. I also set the idle AFR using a vacuum gauge so the engine should have “what it wants” now at idle. Todd

  4. #14

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    You probably have something else wrong that's causing the Sniper to react like that. Maybe your ignition timing is wrong or there's a vacuum leak when hot or some other mechanical problem. The IAC shouldn't have any issue controlling the idle with only 388 cubic inches. Sometimes on big race engines we'll have the IAC at zero during hot idle just so it has enough room to control the idle when the engine is cold, but you only have 388 inches and you have a fairly small cam. So that leads me to believe that you have some other issue. If you can't find it right away, then run some basic engine tests. Pull the plugs, run a compression check, verify firing order, pull the valve covers and verify that everything is fine under there, etc.

  5. #15

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    Thanks Andy. Timing is not controlled by the Sniper. Maybe later, but one thing at a time. Mechanically, all sound, less than 5K miles on the engine, rock solid 15” of vacuum at idle with old carb, 18° initial timing. Same timing with Sniper, same vacuum at idle. My gut is telling me, I should open the throttle blades a bit, but the instructions for setting the blades vs IAC say different. Also, the fact that when the handheld reports IAC position at 0%, there's a significant suction at the IAC port, like putting your finger over the 3/8” PCV inlet.

  6. #16

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    If you want to open the throttle blades, then do it. The engine will either run better or worse and then you can go from there. What you're describing doesn't make sense, so you must have another variable in the equation that you haven't spotted yet. Just experiment around until you find it. Could be a bad IAC motor or something else such as a vacuum leak that you haven't spotted yet. You could also have a RFI problem that's causing problems with the IAC.

  7. #17

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    Hmm, here are my thoughts. :-) For whatever reason, IAC is not actually where the ECU/handheld thinks it is. If it were at 0% or close to 0%, I shouldn’t feel as much vacuum as I do at the IAC inlet. So for this, I think bad IAC or interference. I’ve made sure to separate all harness wiring from all other electrical, plug wires, etc., all good grounds, + & - back to battery, should not have any ground “loops”, etc. Battery ground, chassis ground, engine block ground, body ground, all back to a common point.

    Say I had a vacuum leak, if it was idling low, and the IAC was “adding air”, I'd think this would hurt the idle and maybe even stall? Here's the reasoning for this; ECU does not know about “extra air” coming in, but it can add fuel to hit the Target AFR, assuming it senses it is lean due to vacuum leak. Then IAC could add more air to try to increase idle RPM? If I check the Learn Table, would I see it adding fuel at idle if the above scenario is happening? Thanks.
    Last edited by Wrenchhead67; 09-09-2019 at 01:22 PM.

  8. #18
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    May 2018
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    I'm experiencing the same issue! Please let me know once you've figured out the solution.

  9. #19
    Join Date
    May 2018
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    Update: in my application, I was having EMI issues. I ran the magnetic pickup wires with my coil wires, which were causing me to have these issues. Separated them and then drove the car with no problems.

  10. #20

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    Good you got it figured out. From what I've seen, most "weird" Sniper problems are user installation errors where the Sniper wires are bundled in with ignition wires. The RF interference causes a lot of strange behavior. I pretty much assume now that if someone reports their Sniper is acting weird then they should double check all of their wiring. Both connections as well as location and closeness to any ignition wires.

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