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Adjusting TBI idle?

Discussion in 'The Garage' started by skratch, Apr 27, 2004.

  1. skratch

    skratch 1/2 ton status

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    How in the blue blazes do i adjust my idle?

    I've rebuilt the throttle body, all new components aside from the injectors, replaced all the gaskets, done evrything obvious even disconnected the throttle to make sure it wasn't the problem, but my rig still idles way high and smells like she's running super rich. There are however no codes in the computer right now either. I thought it might be a vacumm leak but haven't been able to find anything to support this.

    The only engine mods right now are Edelbrock headers, and an Accel coil. She's idled like this since the new engine was stuck in her 8 years ago. And I am not going to go through another tranny because of it!
     
  2. 4xcrazy

    4xcrazy 3/4 ton status

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    I have TBI on mine too, as far as i knew, the idle is adjusted by the computer, so if there is a problem, it's got to be something giving a bad reading. You replaced the Idle Air Control valve inside the tbi unit too?
     
  3. skratch

    skratch 1/2 ton status

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    Every sensor in the TBI or related to it has been replaced over the past couple years and still no change.

    I think I may just take it to the shop and have it done this time. /forums/images/graemlins/dunno.gif
     
  4. bleedchevy

    bleedchevy Registered Member

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    i belive there is an idle adjustment torx style screw on the drivers side under a little rubber plug on the front of the tbi at least thats how i adjusted it not sure if its the correct way, but it made a difference at idle
     
  5. skratch

    skratch 1/2 ton status

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    I'll give that a look see in the morning, thanks! /forums/images/graemlins/waytogo.gif
     
  6. Wingnutt

    Wingnutt 1/2 ton status

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    Be careful on how much you speed things up, the computer is apt to get a little touchy about it. When you open the throttle a bit, it will change the TPS voltage, and the computer will try to compensate by opening the IAC less resulting to give a richer mixture (the computer sees a slightly opened throttle as mild acceleration). This can result in a surge at idle because the computer can't make up it's little mind whether to give pirority to the increased TPS voltage (which it sees as a slightly opened throttle) or the rich O2 readings (resulting from the lowered IAC readings). So it trys to compramise between the two, resulting in a surging idle. Did that make ANY sense? There is a real fine line between raising the idle and going a bit to far and ending up with a surging idle.

    Before you go fiddling around with the idle speed to much, check you O2 sensor and IAC. These two guys are responsible for you idle mixture and speed. IIRC, the computer will try to command a 600-650 RPM idle in neutral, and a tad lower (500-600) in gear.

    To properly change your idle speed, you've got to re-program your chip. I ran into a lot of these same problems when I installed a Holley 670 CFM TBI a couple of months ago due to the larger injectors and throttle plates and I had to iron them out for myself. You how-ever shouldn't have any problems because your TBI is stock and all you did was a simple re-build. Check to make sure that everything else is working correctly.

    Oh yea, one more thing. If you have a computer and don't have it yet, download WIN ALDL. It's a hail of a diagnostic tool.
     
  7. skratch

    skratch 1/2 ton status

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    Thanks for the info, I've been meaning to get a Windows laptop to run ALDL on.

    I'm going to try a couple more simple things and if I can't get it, she's headed down to Firestone to get looked at.
    I don't have the desire to mess with this problem anymore, I've been fighting it for several years and gotten nowhere.
     
  8. BurbinOR

    BurbinOR 3/4 ton status

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  9. skratch

    skratch 1/2 ton status

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    Man that Third Gen site seems to have all the answers for this engine.

    Thanks, I looked but didn't find that one. /forums/images/graemlins/waytogo.gif
     

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