RPM's Hanging Up!

Discussion in 'Trucks and Trailers' started by Stinger, Mar 14, 2001.

  1. Stinger

    Stinger LawnSite Senior Member
    Messages: 252

    I have a 1999 Chevy 3500 srw with a Vortec 350/410 gears
    and auto tranny. The truck idles 300 to 400 rpm higher than normal at times. It seems to pulse or rev up on it's own. I had the truck looked at by the dealer 2 times and they can't get the problem to occur while being hooked up to the computer. The throttle body was cleaned and I still have this problem happen several times daily. I think it is something to do with the a/c compressor kicking up the engine idle when the defrost or a/c is used. Does anyone know what could be causing this to happen? Any insight would be greatly appreciated, thanks!
  2. 4x4k20

    4x4k20 LawnSite Member
    from ga
    Messages: 148

    it is normal for this gm has it to where you use the defrost the ac compresser cuts in to mix cold air with the heat to prevent mostiure build up the compresser when it cuts in the computer raises the idle up look in you manuel it should say something in there about this if you want to you can unplug the wire to the compresser thats what i do during the time that i dont use the ac
  3. plowjockey

    plowjockey LawnSite Senior Member
    Messages: 332

    I believe the reasoning behind the a/c compressor running when you use the defroster is so that during rhe colder months the compressor will at least be run some of the time thus lubricating the inner parts.

  4. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    Stinger-the fix is-turn off the defrost-LOL
  5. Stinger

    Stinger LawnSite Senior Member
    Messages: 252

    Thanks for the replys, but the engine revs high enough on it's own that I allmost ran into someone while at a stop light. Plus hooking up a trailer is more trouble than it should be. I really have to ride the break or the truck will pull it's own self. The A/C and defrost was left off all day and I still experianced the same problem.
  6. Jeffrey Thomas

    Jeffrey Thomas LawnSite Member
    Messages: 8

    Does your truck have a mass air flow sensor? If so have it checked out.I had the same problem with a camero and that was the problem. Good luck.
  7. Albemarle Lawn

    Albemarle Lawn LawnSite Bronze Member
    Messages: 1,544

    Tell them...

    "Fix it, get it right, no excuses, and don't call me until its right!"

    And ask for a loaner vehicle. If you have a loaner they will invariably fix it faster and fix it right.

    Its not your problem, if its under warranty it's GM's problem. That's why you bought a new truck. If you wanted to tinker you could have bought an older truck and saved thousands!!!

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