Frustrating cold idle problem ?

Discussion in 'GM Powertrain' started by JTWard, Aug 30, 2013.

  1. JTWard

    JTWard Rockstar 3 Years 500 Posts

    I have a 1990 Chevy 1500 Silverado, 305 w/ TBI injection. New Injectors, fuel pump & tank & filter. Idle is way too low when started, So I installed a new "Idle Air Control Module" but it made little difference. Last month I had some electrical problems that wound up being a bad EPCM and we installed a new EPCM and calpak chip. But no matter what I do, I can't find this low Idle gremlins. I've looked for a vacuum leak but I can't find it and the EPCM doesn't leave any trouble codes as I have check five times now. I'm out of ideas now ???? Thank you !
  2. ChevyBoy2009

    ChevyBoy2009 Rockstar 4 Years 500 Posts

    Have you took off the throttle body and actually cleaned it out? some sea foam through your brake booster vaccum line and see if that helps also...maybe it will help clean the gunk out and idle better
  3. JTWard

    JTWard Rockstar 3 Years 500 Posts

    well everything we've found so far shows a clean, non sludge engine internals. When we put new head gaskets on everything was spotless ? We've cleaned everything we've touched so far, But I can't figure out this last nagging idle problem. I'm going to try squirting a little carb cleaner around the engines intake manifold to see if I can locate a vacuum leak ? Thank you !
  4. ChevyBoy2009

    ChevyBoy2009 Rockstar 4 Years 500 Posts

    Ya it does kinda sound your getting a small vaccum leak...those are the worst ones to find!
  5. JTWard

    JTWard Rockstar 3 Years 500 Posts

    Well even shooting carb cleaner around the intake manifold might work, But I'm doubtful as we just install new gaskets when we did the head gaskets last year. It doesn't leak and fluids, so if there is a flaw or crack, and I'm not saying there is, it sure is hiding pretty well.
  6. edsmagichands

    edsmagichands Member 2 Years 100 Posts

    sounds more like you might be a little "fat" typically a small vac leak would increase idle. try adding propane through throttle body,idle up its lean, down its rich. don't forget MAP & MAF sensors. i' don't remember if they put MAF on the 90's but a dirty MAF will cause idle issues. also don't know anything about the "chip" but any time you "tweak" a PCM you are asking for ghosts to appear.

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