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Thread: Pls I need help with idle, can't figure out why it won't idle

  1. #1
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    Pls I need help with idle, can't figure out why it won't idle

    I've tried to tune idles on couple of evenings and I give up. I have very unstable idle. Often it becomes "hunting idle" and eventually dies, especially coming to a stop. Then another times it is fine.
    Sometimes it wants to idle at 0 rpm, IAC drops to 0 too. Sometimes it idles at 0-5* advance, and often at 14*. There is huge lack of knowledge and understanding from my side.
    Please take a look at my log. You can see it tries to idle at 138rpm this time. Timing at 14*.
    I have 80mm BBK throttle body, 383ci, cam is 227/235 116+6, 3-bar OS, 90lbs injectors.
    Please, need some advices...
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    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  2. #2
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    I verified that 14* is forced by Idle overspeed spark correction (22* plus -8*). But I cannot understand why it wants to idle at 0 rpm or 63rpm or sometimes at 138rpm (and IAC drops to 0)...
    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  3. #3
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    Not very scientific in this forum, but start with adding 30% to your Base Running Airflow table.

  4. #4
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    I have tried to adjust RAF table both ways. If you looks at the log, at some points it wants to have 2-3g/sec, while in base RAF it is 11g/sec...
    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  5. #5
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    Anyone has any idea why sometimes idle desired rpm and airflow decrease to 0?
    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  6. #6
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    Another question is, what commands 0* timing after startup, around 25 seconds? Cat lightof tables are zeroed already...
    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  7. #7
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    Change your idle rpm to 850 or 900 and see if it will idle. 700 is low for your setup. After you get it dialed in you can try lowering the idle.

  8. #8
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    Yes I already tried that, now I lowered it back after adjusting throttle with adjuster screw, now it idles good MOST of the time, but sometimes still starts to "hunt".
    I have 3 unexplainable issues:
    1) timing near 0* after start, for some 15-25 seconds
    2) desired idle RPM sometimes drop to some stupid value like 63 or 75 or 138rpm
    3) desired idle airflow drops to some 4-5g/sec at the same time
    Where to search for clues?
    LS1 383ci 98' FBody, turboed, 00' PCM, 4L80E, 90# FIC injectors
    110ci Nissan 200SX, 25psi, 370whp

  9. #9
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    Could startup flare control (under spark advance) be causing an issue?

  10. #10
    Couple of things I noticed:

    1) It looks like you're averaging close to 70 kPA at idle. That cam should be in the 50s maybe even 40s. My cam with 16 degrees of overlap is in the high 60s. You fueling, timing, and airflow are are off if you have wild swings in the idle. Plus, once you get your airflow and timing set, your kPa should drop.
    2) Check for vacuum leaks. You have some wild swings in your MAP reading. I have a much bigger cam in a smaller motor and my MAP readings aren't that unstable.
    3) Change your Idle Spark for P/N and Gear to 22 across the board. Start there. It's weird your spark isn't moving. Did you disable it with the VCM bi-directional controls in the scanner while logging? Usually it's not flat-lined.
    4) Raise your idle to 850 so it won't die. You need it to live so you can adjust things like the Spark and A/F. Use the bi-directional controls in VCM to lean it out a little more (though your wideband is reading 16 - I wouldn't trust it at idle). See what that does if you lean it out or fatten it up. You can move in half point steps from say 14.7 to 15.2 which is a 5% fueling difference. I'd also set the timing where you want it. And I think 20-22 would be good for that cam at idle.
    5) Adjust your TB to under .65V (closer to .45V would be good) and reset TPS; you'll have to log it to see where it is. You need to shut your throttle blade more to get your IAC counts up if they are hitting 0. This will provide too much airflow and make it unstable as well.