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TBI idle adjustment

Discussion in 'The Garage' started by FlatBlackBurb, Apr 20, 2007.

  1. FlatBlackBurb

    FlatBlackBurb 1/2 ton status

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    okay so I only have till the end of this month to smog my truck. the first time i tried to smog it, it was idling wayyy too high at like 1500 rpm in park. now the guy told me its idling closer to 1200. he said it needs to get below 1100 at least to work. 1000 is the target. how i fixed it the first time was there was a fat radiator leak and there was no coolant in it at all.

    but now what? should i bother adjusting the idle screw? how do i fix a vaccum leak if i have one? could it be the o2 sensor? map sensor? please get back to me i need to smog a.s.a.p. im not going to ahve a lot of time near the end of the month to work on this truck

    thanks.
     
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    You can turn down the idle with the torx screw that is located on the front of the throttle body, but doing so will affect your TPS and IAC values. Ask me how I know.............:doah:

    To see what's going on, you're gonna need to get ahold of an ALDL reader and download winALDL onto a laptop and see what your computer is doing. After getting some sensor values, you'll have a better idea as to what has to be done to get your idle down.
     
  3. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    check the base of the tbi for vacuum leaks.. also wiggle your throttle shaft up and down, see if the idle changes, worn throttle bushings will do this... also pull, check and clean your IAC...

    iirc, the adjustment screw is plugged from the factory and the plug will need to be removed to access the adjustment screw...
     
  4. FlatBlackBurb

    FlatBlackBurb 1/2 ton status

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    how do you know eh? any tips for getting the cap off that seals up the idle screw? should i just mess with the idle for now just to smog it and fix the "real" problem later.
     
  5. sope

    sope 1/2 ton status

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    1000 is still way to high. Don't bother with the idle screw untill you fix the problem. It's posible that the temp sensor is fried after overheating. This is a guess but temp sensors are cheap. This may not cause a code and would cause it to idle high when warm. Hard to diagnose without seeing it but check for vacume leaks first.
     
  6. FlatBlackBurb

    FlatBlackBurb 1/2 ton status

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    okay how/where do i check for vaccum leaks? im thinking it might have something to do with the o2 sensor as well. should i just get both? wheres the temp sensor locateD?
     
  7. sope

    sope 1/2 ton status

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    To check for vacume leaks, first listen for a hiss and do a visual to see if there is a bad hose or a hose off. The PCV plastic hose from the throttle body to the valve and the rubber ends on it are a common problem. If you can't find anything spray liquid around the base of the throttle body and the edges of the intake manifold where it meets the head. Also spray around the hoses where they meet the throttle body and the throttle shaft. If there's a vacume leak the RPM should drop when you hit the spot because it tempoarily seals the leak. Depending on the liquid you use it could rais the RPM. Temp sensor is a two wire sensor near the thermostat housing. It screws in to the intake manifold. If the cap has already been removed for the idle adjustment you could try backing it off but if this used to run OK for you it's not going to be the problem. Honestly if you can't find it this way you should probably bring it to someone that can scan it. There are several other things it could be but parts replacing will probably cost you more than to get it diagnosed. I'm sure there will be other sugestions. That's all I could think of right now.
     
  8. FlatBlackBurb

    FlatBlackBurb 1/2 ton status

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    is it safe to use brake cleaner instead. i have a bunch of it here but no carb cleaner...
     
  9. sope

    sope 1/2 ton status

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    Yea. Brake cleaner can give off some pretty bad fumes so don't spray it on the exhaust.You can use water if you want. I usually use air intake cleaner,
     

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