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Thread: Negative timing at idle. Need some help

  1. #1
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    Negative timing at idle. Need some help

    So the car is a LT1 Stingray and it is pulling negative timing at idle. It also has some random miss fires that I am hoping is related to the timing issue (changed plugs and wires already). We added long tube headers and a ported throttle body. Since there is no kr I'm guessing the ECM is just pulling timing to bring the idle down from the ported tb? Any other ideas on what it could be?

    If it is an issue with the tb does anyone have any good ideas for adjustments? Should I bump up the throttle area limits a little bit? Its the stock size but it is ported. I've switched between two ported units and it didn't change anything. The original was sent back as a core already.

    Should I bump the idle up a bit?

  2. #2
    Senior Tuner Higgs Boson's Avatar
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    its the throttle body, I have had that issue before also with certain brands of ported TBs. did you use a second tb ported by the same people? try another brand or put a stock one back on, they really don't do anything anyways.

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    The stock tb is gone already. There has to be a way to adjust for this with HP right? Should I bump the idle or add some surface area to the throttle area limits?

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    A ported TB and headers shouldn't cause that issue. It is most definitely the ported TB. If done incorrectly it will let too much airflow by the blade at idle and the ECU will react by pulling timing to meet the target idle and target torque value.

    This is of course assuming you haven't touched your Torque Coefficients. Get a stock TB from a friend and swap it on. Since the GenV's are torque based, you can't force the TB to close at idle via a table. If you lower the Torque Coefficients it's still going to pull timing to bring the idle speed down. If you force the timing in the minimum spark tables you will have a run away idle rpm issue.

    Who ported your TB? A reputable shop would know how to properly port a TB. Have any pictures of the port work?
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    It's a V-max system. We installed plenty of them without issue. I bumped up the torque tables by 10% when I added the headers but removed it to see if it was something I did. Didn't change so I went back to the modified tune.

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    Quote Originally Posted by JASON11WS6 View Post
    It's a V-max system. We installed plenty of them without issue. I bumped up the torque tables by 10% when I added the headers but removed it to see if it was something I did. Didn't change so I went back to the modified tune.
    Are you using the motor and TPS sensor from your stock throttle body on the Vmax? Or did it come with one? I've seen on a 2017 SS Camaro before where if the TB motor and TPS are not kept together, they will be mismatched and cause idle problems. Apparently each TPS is configured to match the motor. I think the Tech 2 w/MDI can recalibrate/match them together if you happed to have mixed them up.
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    That really sounds like the problem but I don't have the stock LT1 throttle body at the moment. HP doesn't give us anyway to adjust this?

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    Quote Originally Posted by JASON11WS6 View Post
    That really sounds like the problem but I don't have the stock LT1 throttle body at the moment. HP doesn't give us anyway to adjust this?
    They do not. And I haven't seen the tech2 MDI capability myself, but I read it somewhere on Corvette Forum that someone had it done by the dealer but I can't find the thread. I do know that the Throttle Body Position Sensor Cover and Motors are paired together and calibrated to each other. They can be moved to any throttle body as long as they are kept together as a pair. Now that said, there are cases where people have mixed them up without issue, but that could be that they had a similar calibration range that didn't cause a problem. It also seems to be more likely on 2017+ vehicles but I can't confirm it is only limited to 2017+. The effect of having a mismatch will be a surging idle, along with either a too high idle or too low of idle. Or both in different airflow situations.
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    I had a tech with a scanner relearn the tps to the throttle body. Took two minutes and fixed the issue. Wish HP could do this

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    Quote Originally Posted by JASON11WS6 View Post
    I had a tech with a scanner relearn the tps to the throttle body. Took two minutes and fixed the issue. Wish HP could do this
    So the negative timing at idle most of us are experiencing might be due to not having done a TPS relearn after switching throttle body?
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    It's called the cleaned throttle reset in hpt. Key on, engine off and then perform. Everytime the ECM is flashed this should be done. Helps Dial in the idle too.

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    What channel do we log to make sure it completes? The only one I see is (Pedal/throttle test complete).
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    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by GHuggins View Post
    It's called the cleaned throttle reset in hpt. Key on, engine off and then perform. Everytime the ECM is flashed this should be done. Helps Dial in the idle too.
    that doesn't solve this particular issue.

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    I seem to be having this same issue after replaceing stock ported tb with the new 95mm one. Can this be reset in HP tuners? I no longer have the stock tb. I have a 2016 Camaro SS A8. I have attached a log of start up and idle.


    Attachment 84510
    Last edited by Brianw36; 10-29-2018 at 04:18 PM.

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    This was an older thread but just wondering if people are still having this problem with adding different tb. Or is the hptuners clean trick helping this issue?

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    This might be because you are letting more air in. Did you change the for the size in the etc area scalar?

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    Quote Originally Posted by JASON11WS6 View Post
    This might be because you are letting more air in. Did you change the for the size in the etc area scalar?
    Yes it was updated for the larger size.

  18. #18
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    Quote Originally Posted by Brianw36 View Post
    This was an older thread but just wondering if people are still having this problem with adding different tb. Or is the hptuners clean trick helping this issue?
    TriPinTaZ explained in post #6

    JASON11WS6 confirmed in post #9 ... someone with tech2 scanner has to re-calibrate the Throttle body motor with the TPS.

  19. #19
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    Quote Originally Posted by ZeroBoostBuick View Post
    TriPinTaZ explained in post #6

    JASON11WS6 confirmed in post #9 ... someone with tech2 scanner has to re-calibrate the Throttle body motor with the TPS.
    Ok. So HPT can't resolve it I need to find someone with a tech2 scanner. I take it that is something a chevy service dealer would have. Would a normal independent shop have one. I don't take me car to the dealer ever.

  20. #20
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    Quote Originally Posted by Brianw36 View Post
    Ok. So HPT can't resolve it I need to find someone with a tech2 scanner. I take it that is something a chevy service dealer would have. Would a normal independent shop have one. I don't take me car to the dealer ever.
    Check out post #11 above.