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Why does the idle fluctuate.....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ben, Jan 20, 2004.

  1. Ben

    Ben Registered Member

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    Why does the idle fluctuate.....
    I'll give as much info on the problem as possible hoping I we can figure it out. 84 K5, 350, Q-jet carb.
    During the warm months, no problem. When it's cold, problem.
    I have no heat riser, no smog devices, no EGR, no warm air duct, etc. KN filter sitting on the carb with an electric choke.
    When I first start up, idles on high as it should, kick it down and it idles around 700. Drive around , come to a stop and the idle goes up to around 1100. Kick it down and it's 700 again for a few minutes then again to around 1100. The carb gaskets are tight, saturated the hell out of the carb area with carb spray looking for a leak, none found. The vacuum advance is hooked up to vacuum at idle port. The power brake vacuum line is connected as is the choke pull off line. All other ports are plugged. I'm using a KN air breather for the valve covers so no PCV. When the engine is warm, the choke is fully open. So, I'm confused as to why the idle fluctuates. Any ideas? Thanks! Could using the open air cleaner cause the idling problems? It's COLD here!
    It's so cold that we can hang meat outside!
     
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Next time it does it, pull off the air cleaner and look down into the venturi where the butterflies touch the venturi wall(while it's still running). Got a thick white ice build up? That would cause idle problems and you'd be amazed how easily it forms. Cold air rushing thru a thin gap (between the butterfly and carb body) freezes up really easy. /forums/images/graemlins/thumb.gif
     
  3. lukebaby1

    lukebaby1 1/2 ton status

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    Does your truck still have the AC hooked up, If so, could be the fast idle solenoid is actuating. It will actuate if you have the controls on the dash to defrost. /forums/images/graemlins/thumb.gif
     
  4. R72K5

    R72K5 Banned

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    try sucking the carb out hold open throttle and slap choke shut on her for a coupel seconds and then let choke open, tighten up all the air horn screws and also the mount bolts too first though
     
  5. 89Jimmy

    89Jimmy 1/2 ton status

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    Had a similar situation with my holley carb, I added a secondary throttle return spring and my problem went away.
    John
     

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