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305 tbi cold idle stumble


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  • 305 tbi cold idle stumble

    1987 silverado equipped with a 305 TBI. Mods include: TBI Spacer and Injector Spacer, adjustable fuel regulator set to 13 psi, open element filter, and dual exhaust. The truck idles very rough and rich when first started, especially now that it is cold out. Once it warms up, it idles good. With snow on the ground, you can see black deposits when warming up so I am assuming it is rich.

    I have replaced the Coolant temp sensor since I thought that would have been an issue but it did not help. I think the TBI Spacer may have something to do with it. When the truck was stock it did not have this issue. No, this is not a vacuum leak symptom.

    It's annoying and wastes gas. If I did not know it had fuel injection, I would think it had a carb the way it runs when warming up.
    Last edited by chevymotocross; 01-29-2010, 05:53 AM.

  • #2
    Re: 305 tbi cold idle stumble

    clogged air cleaner or bad temp sensor...

    Not sure about the TBI systems, but typical LS1 injection systems run in open loop (no O2 feedback)when cold. Once they warm up, they use the O2 feedback to adjust fueling.

    If you are too rich when cold, it is either too little air or too much fuel. A faulty temp sensor (coolant or air intake)could be a contributor, by telling the system it is colder out (than it is) which typically will inject more fuel.


    • #3
      Re: 305 tbi cold idle stumble

      I already replaced coolant temp sensor with no luck. Air filter is clean. I'm thinking maybe it needs a tune for the mods I did or maybe a 3 wire o2 sensor so it goes into closed loop quicker.