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Thread: Rough hot idle but smooth cold start

  1. #1
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    Default Rough hot idle but smooth cold start

    Hi all,
    I'm fighting with a rough idle when the car warms up above 68-70C ECT. It runs in OL all the time and is MAFless. Not exactly sure where I should start. I don't see any major changes at that temperature.
    The engine starts fine when cold and idles really smooth without any rocking until it gets warm.
    AFR is around 14.2 when warm. The car has a mild cam and ported heads and idles at 800rpm.
    Thanks
    Alex

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  3. #3
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    Thank you Joe,
    I'm familiar with some of these threads and checked out the ones I haven't read yet. I have set up my idle based on them already.
    I couldn't seem to find anything directly related to my issue, though. I'm sure that there are many indirect influences but if somebody had a similar problem, maybe they can give me a hint where to start.
    Thanks
    Alex

  4. #4
    Member O1Z06's Avatar
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    Just a shot in the dark, is your idle speed set to one value, cold to warm.

    Post a copy of your tune.
    2001 Z06 512K Road Runner COS5
    LSx 427, Comp 7075 TT in progress

  5. #5
    Lifetime Member minytrker's Avatar
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    Quote Originally Posted by Alex99 View Post
    Hi all,
    I'm fighting with a rough idle when the car warms up above 68-70C ECT. It runs in OL all the time and is MAFless. Not exactly sure where I should start. I don't see any major changes at that temperature.
    The engine starts fine when cold and idles really smooth without any rocking until it gets warm.
    AFR is around 14.2 when warm. The car has a mild cam and ported heads and idles at 800rpm.
    Thanks
    Alex
    Post your tune and list all your mods. A data log of cold and hot idle would also help. Its hard to help without knowing anything about your vehicle.

  6. #6
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    Alex_baseline COS5 rebuilt trans w_3rd TCC_0298.tun

    here is my current tune
    Thanks
    Alex

  7. #7
    Joe (Moderator) joecar's Avatar
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    Alex

    You should set C6001:P0103 to A:1-Trip

    ( and look for the immediate presence of DTC P0103 to let you know you are in fact running from the VE table )

  8. #8
    Joe (Moderator) joecar's Avatar
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    Alex,

    are you aware that the 1.000 cells in B3647 will be trimmed to using STFT's...? (this will mess up any attempts at correcting VE)

  9. #9
    Joe (Moderator) joecar's Avatar
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    Hi Alex,

    with a COS you can run adaptive spark (different values in HO and LO spark tables), just set A0002 to 100% (check it by logging ASPARK).

  10. #10
    Joe (Moderator) joecar's Avatar
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    The hot idle problem may be related to the MAF not necessarily being failed.

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