Results 1 to 6 of 6

Thread: Help With Cold Start Idle FAST 92

  1. #1

    Help With Cold Start Idle FAST 92

    Hey guys before I go into this I just want to throw out there that I have ported the IAC opening on my fast 92 tb out a good bit I can probably go more but i dont think I need to at this point. Car is an 02 camaro just upgraded from ls6/ported tb to fast 102/92

    Ok, when I start the car up on a cold start it will start but then either quickly drop down to 200rpm or so and surge until it eventually finds itself and levels out after about 5 secs. The tps reads .53v which is up from yesterday. When I first installed it I would have to hold the pedal open to get it to start, I turned the set screw a 1/4 turn and got it to this point but i cant go anymore due to tps voltage.

    My Iac counts are around 20 hot and a cold start puts them in the 160's. To me at least this says that at cold idle the car isnt getting enough air and with the tb open as far as it can voltage wise I need to force the IAC open more to allow a stable start.

    My issue is I dont really quite understand how to do this. I see the IAC effective area tables but even after reading threads and stickies I'm really not quite sure what to alter. Can anyone give some tips or lend a hand?

    Below is a tuning log of a cold start this morning and a small drive to school along with my current tune. The tuning log I'm havin to feather the throttle a bit when it first started to keep it going then it smoothed out and I let off

    Final Tune pre-fast intake WITH LS3 injectors.hpt


    fast intake scan 1.hpl

  2. #2
    Advanced Tuner JamesLinder's Avatar
    Join Date
    Jan 2011
    Location
    Bella Vista, AR
    Posts
    363
    You should never have to port the IAC opening on a quality throttle body; it will throw off the calibration curve that goes
    with the IAC motor and plunger. You probably have now made it impossible for the IAC to operate within an acceptable
    range to maintain control. I would buy a new TB and not bother trying to tune the one you ported. Life is too short.

    Even a warm start will use 100 to 150 counts, and in cold weather it can easily take almost the entire 300 counts. 45
    counts at warm idle is about right, although 40 to 55 will probably work just fine. You have to have the base spark
    idle tables for in park and in gear correct to provide the proper torque reserve when idling so that it can respond to
    adding and removing of loads from AC, power steering, loading alternator when cooling fans come on, etc.

  3. #3
    Advanced Tuner JamesLinder's Avatar
    Join Date
    Jan 2011
    Location
    Bella Vista, AR
    Posts
    363
    If you have a quality TB, the IAC table values will not have to be changed if you are using the same OEM IAC motor/plunger.

  4. #4
    Senior Tuner DSteck's Avatar
    Join Date
    Mar 2008
    Location
    St. Louis, MO
    Posts
    4,856
    Quote Originally Posted by JamesLinder View Post
    You should never have to port the IAC opening on a quality throttle body; it will throw off the calibration curve that goes
    with the IAC motor and plunger. You probably have now made it impossible for the IAC to operate within an acceptable
    range to maintain control. I would buy a new TB and not bother trying to tune the one you ported. Life is too short.

    Even a warm start will use 100 to 150 counts, and in cold weather it can easily take almost the entire 300 counts. 45
    counts at warm idle is about right, although 40 to 55 will probably work just fine. You have to have the base spark
    idle tables for in park and in gear correct to provide the proper torque reserve when idling so that it can respond to
    adding and removing of loads from AC, power steering, loading alternator when cooling fans come on, etc.
    Quote Originally Posted by JamesLinder View Post
    If you have a quality TB, the IAC table values will not have to be changed if you are using the same OEM IAC motor/plunger.
    I strongly disagree with these posts. Simply cracking the blade open or drilling the hole out changes the IAC calibration curve. All aftermarket throttle bodies have a different calibration curve to the IAC as well too.

    DSX Tuning - Authorized HP Tuners Dealer
    http://www.dsxtuning.com
    http://www.facebook.com/dsx.tuning
    Just say no to bull s***.
    IF YOU WANT HELP, POST A FILE!

  5. #5
    Advanced Tuner JamesLinder's Avatar
    Join Date
    Jan 2011
    Location
    Bella Vista, AR
    Posts
    363
    If you look at the LS1 and LS6 their will only be a slight difference in the IAC curves in the slightly off idle position. The IAC
    curve is specific to the IAC motor and plunger. A large high quality TB will come with a pre-drilled hole that is the correct
    size so that the OEM IAC curve works as intended. I have played around with a half dozen throttle bodies, and yes if you
    buy the lower quality ones, regardless of how much you pay, they will not work well with the OEM IAC curve because they
    are not made properly. Talk to expert Dan Maslic, he will tell you that the IAC curve should not have to be altered unless
    you should go with a IAC motor/plunger other than OEM, which I am not aware exists anyway. If your TB manufacturer
    provided you with a new IAC curve for "their" throttle body, please post the specifics because I do not think you know
    what you're talking about. Tuning idle VEs and idle MAF are tricky because the exhaust flow rate through the headers
    at this state is minimal, not enough to keep the sensor as hot as optimal and with large camshafts are subject to reversion.
    If you do not get the idle VEs and MAF correct, what is typically a rich tune at idle will behave a little better if you modify
    the IAC curve, however this is not the correct way to fix the rich idle condition.

  6. #6
    Senior Tuner DSteck's Avatar
    Join Date
    Mar 2008
    Location
    St. Louis, MO
    Posts
    4,856
    Quote Originally Posted by JamesLinder View Post
    If you look at the LS1 and LS6 their will only be a slight difference in the IAC curves in the slightly off idle position. The IAC
    curve is specific to the IAC motor and plunger. A large high quality TB will come with a pre-drilled hole that is the correct
    size so that the OEM IAC curve works as intended. I have played around with a half dozen throttle bodies, and yes if you
    buy the lower quality ones, regardless of how much you pay, they will not work well with the OEM IAC curve because they
    are not made properly. Talk to expert Dan Maslic, he will tell you that the IAC curve should not have to be altered unless
    you should go with a IAC motor/plunger other than OEM, which I am not aware exists anyway. If your TB manufacturer
    provided you with a new IAC curve for "their" throttle body, please post the specifics because I do not think you know
    what you're talking about. Tuning idle VEs and idle MAF are tricky because the exhaust flow rate through the headers
    at this state is minimal, not enough to keep the sensor as hot as optimal and with large camshafts are subject to reversion.
    If you do not get the idle VEs and MAF correct, what is typically a rich tune at idle will behave a little better if you modify
    the IAC curve, however this is not the correct way to fix the rich idle condition.
    No, the IAC curve is specific to the throttle body as a whole system. LS6 calibrations are moot because they use electronic throttle bodies and consequently the IAC vs. effective area definition is not used.

    Crack a throttle body open, and suddenly the IAC curve doesn't properly line up with a factory calibration for it. Enlarge the hole in the blade, and the same thing happens. The IAC vs. effective area is meant to define the TOTAL effective open area of the entire throttle body system, and not just the IAC port itself. That's why 0 counts in the calibration curve doesn't correlate to 0mm².

    I've played around with hundreds of cable throttle bodies spanning stock vehicles to the wildest of cams. I don't need to talk to anybody about this because I understand that the IAC calibration curve is a definition of the system and not a single component.

    I'm biting my tongue about the "you don't know what you're talking about" statement. I guess you didn't realize that O2 sensors have built in heaters to keep them at proper operating temperature despite low exhaust mass flow rates, let alone how the IAC calibration curve is used.

    Answer this... How is the IAC curve calibration still accurate if a throttle body blade has a 6mm diameter hole instead of a 4mm diameter hole while still using the same IAC equipment? Have you ever had a vehicle that needed more air at cold idle even with 310 counts on the IAC?

    DSX Tuning - Authorized HP Tuners Dealer
    http://www.dsxtuning.com
    http://www.facebook.com/dsx.tuning
    Just say no to bull s***.
    IF YOU WANT HELP, POST A FILE!