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Thread: Idle surge

  1. #1
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    Idle surge

    I have a 2001 c5 corvette with a ls3 tsp f35 cam headers corsa exhaust and varraram intake the issue I am have is sometimes rolling to a stop I get idle surge when I come to a complete stop it idles fine also if it starts doing it I can turn car off and back on and it will go away for a bit I checked for vacuum leaks did compression test cleaned Tb replaced manifold gasket and it still does it from time to time any help will be appreciated

  2. #2
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    It's probably something in the tuning.

  3. #3
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    Often surging idles are because it is too rich but it can be many other things too. A log would help to determine
    Tuner at PCMofnc.com
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  4. #4
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    Ok I will attach one when I get home if this does not work but at 11:22 it starts to surge
    Thanks
    Attached Files Attached Files

  5. #5
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    looks like it's hitting a stall limit and then cranking open the electronic throttle or IAC to save it from stalling. Timing jumps around a lot as well. Can you post your tune and the stock version of it?
    Phil K.
    02 Camaro SS 5.7L LS1
    01 Silverado 1500HD 6.0L LQ4 4L80E 78/75 turbo with Flex Fuel

  6. #6
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    Here is the tune don’t have stockjz c5vette tune.hpt

  7. #7
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    So this is a MAF only tune, is this due to the cam? I see your STFT's swing wide on decel suggesting the MAF tune could use some work. Also, under spark/Advance your overspeed and underspeed timing values are weird and extreme. I also turned of DFCO until this is figured out. Try the attached tune for overspeed and underspeed timing values. The big thing is your base running airflow seems weird. I bet if you tune warm-up idle, the stall will go away or at least get a lot better. From cold, log the desired airflow during warm-up. I think there is a detailed sticky on how to do this.
    Attached Files Attached Files
    Phil K.
    02 Camaro SS 5.7L LS1
    01 Silverado 1500HD 6.0L LQ4 4L80E 78/75 turbo with Flex Fuel

  8. #8
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    Idk why it’s maf only and do I just put in the file you sent or do I need to do other things to it also what gets me if it starts to surge I can turn the car off and it will stop also I can drive hours with it not doing it and then it will start acting up

  9. #9
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    Can you look at this tune this is the one in the car now jz c5vette tunet1.hpt

  10. #10
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    The tune you sent is MAF only, I didn't change that. Under Airflow/Dynamic, High RPM disable is set to 100 rpm, which means anything over 100rpm uses only the MAF, no VE table.

    If you do a compare, you will see that I only changed 1) DFCO temp to 284, so it doesn't activate while tuning, 2) Disabled AC bump Tq idle spark because that can do weird things sometimes, and 3) changed overspeed and underspeed spark values. So, yes you can load that tune in, but those changes alone are not going to fix it. You need to tune Base Running Airflow, I bet that is the problem or at least a large part of it. Read the stickies on idle tuning. Basically, log desired airflow as a function of temp, then plug that into your Base Running Airflow Idle airflow table. Then drive and see if it's better.

    I'm assuming this is the tune that came with the car? I.E. no history on why the tune is set up the way it is?
    Phil K.
    02 Camaro SS 5.7L LS1
    01 Silverado 1500HD 6.0L LQ4 4L80E 78/75 turbo with Flex Fuel

  11. #11
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    I swapped to ls3 and the second tune I sent is what’s in the car now so I don’t know why it’s tuned this way from my tuner

  12. #12
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    Bump