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Thread: Surging Idle while Coasting

  1. #1
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    Default Surging Idle while Coasting

    Got the car tuned in pretty well and idling nicely, however I have notice one annoying thing which i can't figure out. For some reason if the car is coasting to a stop at idle it will begin to surge. once you stop the idle tables must change and the surging will always stop, but any time your rolling with 0% throttle at an idle rpm it will surge... Any suggestions on what to look at or change? I have enclosed both a screen shot of the scan, and the tune. File

    I thought it was possibly the fuel or spark cells it was pulling from had drastically different values causing the surge, so i put all the same values in for the timing and smooth out the fuel tables. this didn't help.
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    Last edited by gpr; July 31st, 2013 at 05:17 AM.

  2. #2
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    bump, anyone got any ideas or pointers on where to look? I thought maybe throttle cracker or throttle follower but I am at 0% throttle when the issue happens and the rolling idle tables don't really have anything addressing this issue.

  3. #3
    Joe (Moderator) joecar's Avatar
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    That depression in your VE table (since MAF is failed) at 1200rpm/40kPa does not look right, and may be under-computing airmass... and in your log it looks like spark advance might be being used to attempt to control engine speed...

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    Mine does this too ever since switching to COS5 2bar SOLSD. It was perfect before. I just haven't gotten around to trying to fix it.

    Throttle cracker opens up the throttle if you're moving, so that could be a place to start. Also, the idle spark control isn't active until you stop, so that's another thing to consider.
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    I copied the high and low learned values from the idle section to the rolling idle high and low learning idle correction. This seemed to help with the surging but did not completely eliminate it.

    btw, i did change the VE table at that spot. I had stft enabled, so i'm guessing when logging data that was throwing off the ve calculations?

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    Default Surging Idle while Coasting

    Quote Originally Posted by gpr View Post
    btw, i did change the VE table at that spot. I had stft enabled, so i'm guessing when logging data that was throwing off the ve calculations?
    If you did not account for the stft in your calc_pids file then yes they will cause errors with your VE table. Been there before...
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    Quote Originally Posted by Wheelz View Post
    If you did not account for the stft in your calc_pids file then yes they will cause errors with your VE table. Been there before...
    How do you add the stft into the calc_pids file? i have been using the one posted on here in the calc.maft thread.

  8. #8
    Joe (Moderator) joecar's Avatar
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    OL STFT trimming must be first disabled (before doing tuning)...

    OS: disable B4206.
    COS: disable B4206 (if it exists), and avoid having stoich cells in B3647.

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    Quote Originally Posted by joecar View Post
    OL STFT trimming must be first disabled (before doing tuning)...

    OS: disable B4206.
    COS: disable B4206 (if it exists), and avoid having stoich cells in B3647.
    B4206 doesn't exist in the COS5, it is B4108 to disable stft at idle.

    Why are you not suppose to have stoich cells in B3647? I thought they were all suppose to be stoich values except the last column or two which are richer?

  10. #10
    Lifetime Member Chevy366's Avatar
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    Quote Originally Posted by gpr View Post
    B4206 doesn't exist in the COS5, it is B4108 to disable stft at idle.

    Why are you not suppose to have stoich cells in B3647? I thought they were all suppose to be stoich values except the last column or two which are richer?
    Because Stioch in B3647 in a COS causes stft mode, you need to eliminate all such modifiers.
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