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Thread: Off Idle Stumble - Erratic TPS and RPM Swings

  1. #1
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    Default Off Idle Stumble - Erratic TPS and RPM Swings

    I'm working on a tune for an LS2/T56/E40 swap. It has a terrible stumble off idle often times dying. Letting out the clutch initiates the stumble, slight surging, and then dying.

    I've attached two logs and the tune file. I've included the frames to focus on the issue. What seems weird to me is the erratic and choppy swings in TPS. You can see the TP going up, yet the RPM is going down. Or RPM going up and TP falling down to 18-19% for a split second, then surging back up causing a yoyo effect. The surging is effecting everything like MAP, MAF, G/cyl, spark, fueling, etc, but I think it starts with the TPS activity.

    Driving Log 3.efi
    Driving Log 2.efi
    Original Tune.ctz

    Unfortunately, I did not log the APP and ETCTP, so it's hard to see how the correlation between the two. I can tell you I was not feathering the throttle, if anything, giving it more throttle as I let the clutch out. One last note, the VSS signal is not working properly. That's getting fixed now.

    Driving Log 2 - Beginning at frames 1231, 1618, 1831
    Driving Log 3 - Beginning at frames 414, 683, 1149, 1486, 1719, 1950

    Anybody have thoughts on the TPS activity?
    Last edited by LastCall; February 24th, 2017 at 12:10 PM.
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

  2. #2
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    Anybody?
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

  3. #3
    Joe (Moderator) joecar's Avatar
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    I'm looking, but I don't know yet what I think... ETCTP helps...?

  4. #4
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    Thanks JoeCar.

    Unfortunately I did not log APP or ETCTP. Going to try and get another log in the next few days to compare the two.
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

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