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random fast idle

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sparky, Jul 12, 2001.

  1. Sparky

    Sparky 1/2 ton status

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    San Antonio(summer) Texas A and M (school year)
    Lately when i get my truck hot it wants to idle much faster than normal. I have not checked anything yet, but I'm planning on checking the timeing and some stuff on my q-jet. Any other ideas? It normaly idles at about 650 rpm in gear and 750 out of gear. When it gets hot it wants to idle at 800 in gear and about 1200 out of gear. At first it was doing it randomly every now and then, but now it does it every time I drive the truck. Maybe something to do with the metering rods in the carb or something? It seems to have gotten a little harder to start in the morning too. It fires up the first time every time, but then wants to die unless I give it a fast idle with my foot. Other than those two problems it drives like it always has. Anyone know what else would cause this problem?

    Spaky

    PS: OH, and its not the fast idle cam lever thingy sticking on the carb. My choke does not even beging to close in the summer in south texas.

    When all else fails... Check the blinker fluid.
    78 K-5
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Have you checked for vacuum leaks? The start then stall is a telltale vacuum leak sign, but the faster idle is choke. Make SURE the shoke blad is vertical when it is running at fast idle. Also check to see how much "slop" the primary throttle shaft has, not in out, but side to side/up and down. That will cause random idle speeds though typically, not constant high idle. Check timing like you said, could be sticky weights.

    Dorian
    My tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
    No anti-theft measures on your truck? No pity when its stolen
     
  3. buggybuilder

    buggybuilder Newbie

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    The Fast Idle cam lever thingy? Sorry man, just had to give you a hard time. I'll check it out with you when you arent working. Call me later.
     
  4. Emmettology 101

    Emmettology 101 3/4 ton status

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    Does sound like a vacuum leak... Get some carb cleaner or a small propane tank and spray it aroud the intake and carb base while it is running and see if the idle changes. If the idle does change(goes down and the engine seems to bog) then you have a leak..

    <font color=green>MIKE</font color=green> - "Hukd on fawnics,werkd fer me!"
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  5. 85GMCJimmy

    85GMCJimmy Registered Member

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    This might seem really simple, but when it does this is the AC off or on? sometimes when your turn it off you will not get the switch all the way to off, if it is not than it will cause the truck to idle fast. Mine did this all the time when i did not have AC when i just used the vent, and when i went to turn it off, i would bring the switch all the way to off, just an idea. Some problems can be very simple. I could be wrong, but it was just an idea.
     

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