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Thread: Negative Idle Timing.

  1. #1

    Negative Idle Timing.

    What causes negative idle timing? I have adjusted the timing at idle, I have checked my fuel trims, I have ran a maf only tune, checked my maf, changed spark plugs done everything I can think of.

    Whenever the car is at idle, timing is roughly -5 degrees. She idles fine, drives great, no issues at all but for someone reason the idle timing is negative.

    This is on a 2006 lsj TVS 80lber car. Any ideas guys?

  2. #2
    Senior Tuner cobaltssoverbooster's Avatar
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    need your curent tune file and a scan preferably catching your idle.
    do you have the bigger tb?
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  3. #3
    Advanced Tuner imphat0260's Avatar
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    Post the file? Are you saying that it is always negative, or it hunts to negative?

    P&P Tuning
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  4. #4
    The throttle body has been cleaned, but is 100% stock and working properly. At idle, ALWAYS the car has negative timing. I will put up a scan of the car to see if it helps. The tune won't help much, because I can change the high octane / low octane timing all I want, and it doesn't change anything. I can also adjust the idle spark advance to all 10s or all 15s and nothing changes. I just adjusted the tune again, I will see if it changes and will report back with a log.
    Last edited by 06cobaltss/sc; 03-31-2012 at 02:41 PM.

  5. #5
    Advanced Tuner imphat0260's Avatar
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    Quote Originally Posted by 06cobaltss/sc View Post
    The throttle body has been cleaned, but is 100% stock and working properly. At idle, ALWAYS the car has negative timing. I will put up a scan of the car to see if it helps. The tune won't help much, because I can change the high octane / low octane timing all I want, and it doesn't change anything. I can also adjust the idle spark advance to all 10s or all 15s and nothing changes. I just adjusted the tune again, I will see if it changes and will report back with a log.
    The tune will help.. WE can see what else may be affecting it, such as a modifier or something of that nature....

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  6. #6
    Advanced Tuner gn2beatu's Avatar
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    If you have negative timing at idle, it is because the computer is trying to lower the RPM.

    Here are some causes that may or may not apply to you, but are general causes depending on the type of TB being used.

    You may have an overported TB
    The throttle screw is opened up too much
    Is there a hole in the TB, is it too large?
    It could be sticking and not closing all the way
    Spring tension could be too light not closing

    etc, etc, the gist of it is that the ECM is trying to reduce idle. Negative timing is not good, and can cause headers/ex manifolds to glow, or be too hot, and or super high EGT's. If it gets too bad, it can be bad on the seals in the head too. I would find and fix the issue.
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  7. #7
    imphat0260 - all multi's are zero'd out, except for the danger zones. IE anything above super high iat2's pulls timing, super high ect temps, etc.

    gn2beatu - throttle body is stock, throttle body is in 100% perfect working condition, this throttle body on another car will not replicate the issue, it's not the throttle body.

    I am going out in a little bit to fiddle with it. I will upload my results here shortly. I am going to try and set like 20 degrees of idle timing to see if maybe the 10 i have now there is something that is pulling out say 12-15 degrees for some reason. Either way I will update this tonight, brb.

    BTW I am on e30 so I can have really high timing in the idle/midrange/max and it won't be dangerous due to the high octane etc.

  8. #8
    Ok here is a quick update. This is odd.

    I started the car cold, first start of the night, instantly started up my scanner. Low and behold the car timing is between 9 and 15, more so between 12 and 15 though. I was commanding 15 and had everything zero'd out for mutli's etc.

    I let the car idle and warm up etc. Everything was fine until 140 degrees when suddenly the timing just shot straight down. The fuel trims were off because the temps change here drastically every night so I adjusted them but it didn't help.

    I am letting the car cool down to see if it has something to do with that. I forced the car in open loop / closed loop with the scanner and the timing didn't change. I will upload that first log now for you. YES I KNOW THE FUEL TRIMS ARE OFF, I ADJUSTED THEM lol.

    Not sure how to add the file on here but here is a log of the car.

    http://www.filedropper.com/fueltrimsoff1

    Think I figured out the uploading part. I changed a few things around on the tune and tried different stuff. No clue whats causing this!

    Edit: I added another log called "negativestill" which is with the fuel trims in line while i was on a maf only tune dialing in the fuel trims.

    Either way in the first file, "fuel trims off1" you can see the rpms increase, the timing drop, the maf lb/min increase and the o2 waves "change". No clue whats wrong though.
    Attached Files Attached Files
    Last edited by 06cobaltss/sc; 03-31-2012 at 10:27 PM.

  9. #9
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    What are your mods? This typically can be adjusted with the over/underspeed cam tables.

    Did you recently change anything with your cams or timing chain? I have seen this happen when the cam/crank is one tooth off.

    I would not let the car idle at that timing too long. Negative timing increases exhaust gas and cylinder temps which will cause big problems if not treated.

  10. #10
    I have a ton of mods, but none that would cause this. No internal engine mods or anything. Just a TVS, 80lbers, injen cai, blah blah blah. The rest don't really matter.

    The exhaust temps "appear" to be fine. I will toss a laser on them and get a semi accurate ish reading when I can. They don't glow red though, everything about the car reads fine. It's just odd.

    Only thing I can think of, is in the vcm suite help section, there is an issue about negative idle timing on the 3800 v6 motors. Maybe that is happening here?

    No clue though...I will keep fiddling and see what I can do.

  11. #11
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    Up the RPM to 900-950.

    0 the PW adders and set Short Pulse Limit to 0.

    See how that works.

    Then if still negative timing try these Over/underspeed timing tables under the "Idle Adaptive Spark Control"


    Also: Do you have the new timing chain tensioner?
    Attached Files Attached Files
    Last edited by HNRClothing; 04-02-2012 at 11:44 PM.

  12. #12
    Not 100% sure if I have a new timing chain chain tensioner or not...I have had this car for awhile and have done so many things over the years with it. I got "new" injector data from a member here that I am trying. I will try your info and his info out and see how it goes. Will update this tonight .

    Thanks for the help guys. I will have logs shortly.

  13. #13
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    Hope the injector data works.

  14. #14
    Anytime I change the injector data it makes my maf off drastically. I would have to rescale my entire maf and that is gonna be a lot of work.

    I guess I could try it but I still don't think that it's going to work. I will keep messing around though and see if I can't get it to change.

    It just makes absolutely no sense that everything is fine, and then it changes. It wouldn't be tuning related if it was fine at one point IMO.

  15. #15
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    If you mess with the injector data of course the MAF is going to skew.

    I said it could be mechanical like the timing chain jumping a tooth, like I have seen before. Any codes?

    Run injector cleaner through your tank, maybe you have a clog or something messing with the fueling.

  16. #16
    No codes, timing is right everywhere besides idle. Mid range it commands exactly what I tell it to, as does it at WOT.

    I doubt there is an issue with the injectors because idle afr is perfect as is the maf, along with wot. There isn't anything indicating that there is an issue with fueling so I ruled that out awhile ago.

  17. #17
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    The car will still command the correct timing with a tooth off or not.

    What about a vacuum leak?

  18. #18
    If I am sure about anything in life...it's that I do NOT have a vacuum leak lol.

    Would there be other symptoms if the timing was off a tooth besides the timing, randomly, changing during idle?

    I just don't get how it can be right when the car was first started, sub 140 degrees, and then off afterwards. If you look at the o2 wave, they changed also. Maybe it has something to do with that??

    I have no idea...but I know FOR SURE there are no vacuum leaks.

  19. #19
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    heres what I seen in your log is your at 190 ect and idling at 940~. in your tune you have it set to idle at 850rpm at 190 ect. so that a overspeed of 90~rpm. looking at your idle base spark is set to 15 across the board. now your overspeed table shows for a 90rpm overspeed conidtion to take away 18 degrees giving you a desired -3degrees advance.
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85

  20. #20
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    so why is your car always idling faster then command?
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85