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  1. #1
    Electronic Ignition!
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    Help with some lt1 tuning tuner pro

    Ok so a few things Iím trying to figure out I swapped a 94 lt1 4l60e into my 78 el Camino motor seems to idle a bit to high around 1200-1300 at idle in drive and about 1500-1600 in park I have no vacuum leaks and tps tests correctly also have a few transmission issues but mostly tied to the vss not being connected to the speedometer but the idle issue not sure if itís a tuning issue

  2. #2
    Fuel Injected!
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    More questions than answers. If you have access to the datastream see what your IAC (idle air control) counts are. This is assuming you are a DBC (drive by cable) system. IAC count should be about 30. If it is zero that you have a vacuum leak because your computer is trying to command zero amount of flow through your IAC valve.
    To confirm that your IAC is actually closed, there is a small orifice by passing your throttle plate that the IAC uses to bypass the throttle plate to control your idle speed. Disconnect your mass airflow sensor and remove the intake duct, then start your car. It might take a little bit but should eventually, within about one minute, start to idle reasonably. Then you can take your finger and plug this orifice and if the idle speed drops to normal the computer is either commanding it open or the idle air control is stuck, broken, wiring is incorrect or the PCM is defective.
    DBW (drive-by wire) is a whole different topic.
    Another thing that can cause high idle is coolant temperature. Look at your datastream and see what ECT is, -40į indicates an open circuit.

  3. #3
    Electronic Ignition!
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    Thank you great info and gives me somewhere to start I’ll try that later today and yes it is DBC I’ll look at my data stream and see what the IAC count is and ECT

  4. #4
    Electronic Ignition!
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    On another note I’m still having some trouble with the transmission not shifting properly stays in second and tcc won’t lock up using flash hack I can command the tcc to lock up and put it in 4th gear that way i need to add a resistor to the vss wire from pcm to switched 12v that’s what Dana said over at lt1 wiring back when he did this harness and tune since I’m not running it to a speedo so worst case scenario I have a th400 to throw in but if I go that route do I need to disable all transmission controls in tuner pro or somewhere else

  5. #5
    Fuel Injected!
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    I do not have much experience with the transmission yet, still trying to get mine perfected. I can share my bin file with you but it is for a 603 operating system. I have a 408 cu in LQ9 LS with a 4L60E transmission.

  6. #6
    Electronic Ignition!
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    Quote Originally Posted by MO LS Noobie View Post
    More questions than answers. If you have access to the datastream see what your IAC (idle air control) counts are. This is assuming you are a DBC (drive by cable) system. IAC count should be about 30. If it is zero that you have a vacuum leak because your computer is trying to command zero amount of flow through your IAC valve.
    To confirm that your IAC is actually closed, there is a small orifice by passing your throttle plate that the IAC uses to bypass the throttle plate to control your idle speed. Disconnect your mass airflow sensor and remove the intake duct, then start your car. It might take a little bit but should eventually, within about one minute, start to idle reasonably. Then you can take your finger and plug this orifice and if the idle speed drops to normal the computer is either commanding it open or the idle air control is stuck, broken, wiring is incorrect or the PCM is defective.
    DBW (drive-by wire) is a whole different topic.
    Another thing that can cause high idle is coolant temperature. Look at your datastream and see what ECT is, -40į indicates an open circuit.

    Thanks this solved it your the man iac count was all over the place did what you said plugged it and idle dropped. I have a few extra spare parts I swapped the iac with a used one I have and that fixed the issue. Now Iím wondering if that somehow affected my transmission and it not shifting correctly

  7. #7
    Fuel Injected!
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    Glad I could to help.

  8. #8
    Electronic Ignition!
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    So back to the transmission it’s not shifting right sometimes it will shift to 2nd or 3rd but everything is off I know my gear ratio that the tune originally had was for 3:42 now it has 3:08 with a smaller tire so not sure if my shift points are out of wack or if it’s internal issues with the transmission

  9. #9
    LT1 specialist steveo's Avatar
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    when you change gearing there are all these vss based transmission tables that need to be corrected. you need to do some math and find the percentage difference between old road speed and new road speed and correct those tables. the commercial tool tunercat has a built in tool that does that for you, or you do it by hand in tunerpro.

    for example there is a table called up/down shift points and it is in MPH. so if it thinks you're going 30mph and you're actually going 35mph (probably pretty close to reality with that change) then the shift will happen at the wrong time.

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