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Thread: idle problem - car stalls coming to a stop

  1. #1
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    idle problem - car stalls coming to a stop

    I have a weird stalling problem that I am trying to fix. My car idles fine just sitting but when I come to a light and push in the clutch to stop, the RPM's will fall and over shoot my idle (850) and the car almost stalls and then the IAC tries to recover and it surges for a few times trying not to stall before it stabilizes at 850 again. Sometimes it flat out dies. The odd thing is, it works fine for about 5-10 mins. every time you start the car. For example. If the car is fully warmed up and I'm driving and I come to a light and motor dies, when I restart the car it works fine for a while. No stalling. Then about 5-110 minutes later, it starts doing it again. I have even raised the rolling idle to 1050. That also works fine for the same time period and then stops making a difference. After a fresh key cycle, idle hangs at 1050 and then drops to 850 after a couple seconds. Once she starts acting up, this no longer works, Car goes straight to stalling upon coming to a stop. I can be at 1500 rpm, and put in the clutch and she'll stall.

    Here some info on my car. 406 ci LS3 with ported 243 heads and Fast 92. Nick Williams throttle body with the remote IAC. I have a very short Air path to the IAC which is hooked up to the vaccum port on the passenger side of the MAF where you usually hook up the PVC line. This is a large orifice so I would think It would flow enough air. Cam is a 239/245 .610/.627 112+2. Car idles fine on its own with IAC off and spark help off. IAC values are low though, around 30. Just revving the car up in Neutral has similar results. Works fine and has a soft landing for the first 5 min. or so and then once the IAC counts fall to 30 and stop dropping, that is when it starts to over shoot after a rev.

    My tuner has tried to fix it but everything he does seems to only affect the way it behaves in those first 5-10 minutes when the problem is not these. Once that magic amount of time or something passes, it starts stalling again.

    heres my current tune.. I'll post a log in a few.

  2. #2
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    here's one. i will log more with IAC in chart

  3. #3
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    more logs

  4. #4
    Tuning Addict WS6FirebirdTA00's Avatar
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    Check the stickies, need more info in the logs like STIT, LTIT, etc.

    This is a very common issue which just plain ol' sucks. The lovely OS is to blame for some of this, assuming there is nothing off in your tune. Then you have to start logging and troubleshooting after the time passes. It can be fixed though.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  5. #5
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    also, I have a 18lb flywheel. Could this have anything to do with it? Voltage at idle on tps is .70v. I will try to log more runs with correct parameters.

    Mike

  6. #6
    Questions..
    What size TB?
    Have you run the RusK idle air scan?

    Match your high octane spark table to the Idle spark advance in park and drive.

    Try lowering your idle air decay in throttle follower, both in gear and P/N.

    Hope this helps.

    Good luck

  7. #7
    Looks like you are trying to run a MAF only file, your High RPM Disable in the Dynamic Airflow is @ 800 RPM. Possibly when the stall is under way then the VE comes back into play as well?

  8. #8
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    Quote Originally Posted by outcastdon View Post
    Questions..
    What size TB? 92mm
    Have you run the RusK idle air scan? no not yet. trying to find time to digest all this info and get some proper logs.
    one other quick question about the TPS voltage at closed throttle. I keep reading conflicting info as to what voltage is acceptable. some say .45-.55v and others say up to .6v and others say it doesn't matter as the computer recalculates closed throttle each time and not to worry about TPS voltage. This computer and harness are from a 2002 Camaro SS. I am reading .70 v. Should I be slotting the TPS holes to get the Voltage down?

  9. #9
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    Quote Originally Posted by ctd View Post
    Looks like you are trying to run a MAF only file, your High RPM Disable in the Dynamic Airflow is @ 800 RPM. Possibly when the stall is under way then the VE comes back into play as well?

    I just looked at what you stated. I have no idea why that is changed. It is at 4,000 in a stock tune. I'll ask tuner if he changed that. Multiple tuners have been in this ECU. One when 1st installed swap to get it running, one when I did heads and cam on that motor, and now this tuner for the 406 LS3. Not sure which one changed that. Current tuner is out of town for a week so I am trying to get the idle right my self to learn what to do. Should I put that back at 4k?

  10. #10
    Originally Posted by outcastdon

    Questions..
    What size TB? 92mm
    Check your ETC area scalar.
    Have you run the RusK idle air scan? no not yet. trying to find time to digest all this info and get some proper logs.
    Try doing this first.
    Then retune.

    At work and can't reopen tune.

    Shouldn't have to slot the TB holes

  11. #11
    Quote Originally Posted by mfilippello View Post
    I just looked at what you stated. I have no idea why that is changed. It is at 4,000 in a stock tune. I'll ask tuner if he changed that. Multiple tuners have been in this ECU. One when 1st installed swap to get it running, one when I did heads and cam on that motor, and now this tuner for the 406 LS3. Not sure which one changed that. Current tuner is out of town for a week so I am trying to get the idle right my self to learn what to do. Should I put that back at 4k?
    No I would not. Maybe try 100rpm to keep the VE off while you figuring the idle out in MAF only.

    If you look at your logs the timing is helping you head for the stall.

  12. #12
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    Quote Originally Posted by ctd View Post
    No I would not. Maybe try 100rpm to keep the VE off while you figuring the idle out in MAF only.

    Please explain further. This is set at 4000rpm in every other tune I see. Why would it be at 800 and why lower it vs. put it back at 4000 where the factory set it. I looked at an old tune of mine from 2011 which is what was in the car for the last 2 years while it was a Ls1 and it was 800 then as well. Looks like the old tuner changed it for some reason and either never changed it back on purpose or because he forgot. What does this affect and why set it at 800? Was it to dial something in and then he forgot to set it back? or is this something people do?

    If you look at your logs the timing is helping you head for the stall.
    i'll check on that thx

  13. #13
    Another question you might ask your tuner is why the BRAF @ idle is 20.70g/sec & your actual idle airflow thru the MAF is in the 11-12 g/sec. Might be a clue as well.

  14. #14
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    That I know He was raising it trying to see if it would make an impact and then My computer ran dead and he had to leave so those cells have to be set back to where they were. Stalling issue was there before he raised them. The idle section in the tune I posted has a lot of temporary changes trying to flush out the issue. it is not a final setup. Here is an earlier tune where everything seemed fine except for the stall. It is Rev, 14. The tune I posted was Rev 25 after lots of changes trying to get something to work. He had to fly out of town and is going to work on it when he gets back.

    The other setting I asked about has evidently been like that since the original tuner tuned the car along time ago. I was curiuos why it would be changed and why would it be anything other than stock.

    The other question that I still can't seem to get a definitive answer to is what Voltage the TPS should read at idle. Here are two quotes from 2 tuners here on HP tuners site with directly conflicting info.


    Soundengineer:

    "on a 98-04 ls1/ls6 pcm... you cant go past 0.55v for closed throttle or you wont enter idle cells and you wont see 0% TPS even with a reset

    If you need more air than .55 volts to idle properly, then you either need to drill a hole in the TB blade or you need to slot the TPS sensor holes and grind off a nub so that you can twist it to set a new 0 position.


    I dont know for certain about other vehicles... anything Drive by wire doesnt give a rats ass as you can just add idle airflow till its happy."

    __________________
    -Scott

    Or

    LSxpwrdZ

    "There isn't a dead set TPS voltage to set the throttle body up at. I alway's adjust the throttle body open until warm idle has a IAC Count of 50. Then I'll reset the TPS by unplugging it and do a key cycle then off and plug it back in. This should reset the TPS % back to 0 for the voltage the TPS Sensor is sending. It'd be nice if we had an option to relearn TPS in the scanner!"


    Who do I believe? I would think before starting any idle tuning, having the right TPS setting/voltage would be paramount.

  15. #15
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    oops here's the tune.

    I will have logs tomorrow when I can get back to working on car.