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Sticking at high idle

Discussion in 'Chevy Trucks' started by owen, Aug 27, 2003.

  1. owen

    owen Member
    from florida
    Messages: 34

    Just bought a brand new 1985 C20, crew cab, 2WD, 454.....ok, my wife thinks it's a rust bucket, but it's new to me:)

    When I give it enough gas to kick down the tranny (auto) into 2nd all acts normal, but after I let up the idle or throttle is stuck real high. Only way I've found to get it normal is to turn off ignition and hit the gas pedal. For some reason it wont idle down when hiting the gas while it's running (even in neutral).

    Also...What does that plastic sliding switch do under the dash that is activated when the gas pedal is depressed about 75%? The gas pedal arm moves it on and off.
     
  2. wyldman

    wyldman Member
    Messages: 3,265

    The little switch above the gas pedal is the trans kickdown switch,which means you have a TH400 trans.

    Sounds like you have a choke problem.If the choke cap is bad,the choke may be coming back on some,and giving you a fast idle.Check the choke to make sure it is off fully.It could also be sticking on something.Take it for a drive with the air cleaner off to try to see what's going on.Familiarize yourself with the fast idle cam,so you will be able to recognize if it is stuck on.

    It culd also be something else holding the throttle open like an A\C stepper.a dashpot,sticky throttle linkage,or even a floor may holding the gas pedal down some.

    Check the choke first,and let us know what you find.

    .....and Welcome to Plowsite :waving:
     
  3. owen

    owen Member
    from florida
    Messages: 34

    Thanks..you nailed it:D

    The choke was stuck on just barely. When I moved the choke back to its normal position the idle went back to norm.

    uhh..what's a choke cap?
     
  4. wyldman

    wyldman Member
    Messages: 3,265

    The choke cap is the black plastic round thing on the pass side of the carb.It is a heat sensitive spring,using either exhaust heat,or an electric heater.When it goes bad,it will fail to come off fully.

    If the choke was just stuck on slightly,it may just be sticky.Get a can of carb cleaner,and clean everything up,and see if it helps.You could also back the choke off some,by loosing the three screws that hold it in place,and turn in towards lean (arrow marked on cap),to help the choke come off fully.
     
  5. owen

    owen Member
    from florida
    Messages: 34

    This one is rivited in place. It looks as though I could twist it anyway as I have done on other cars, but there is a tab that holds the cap in one position.
     
  6. owen

    owen Member
    from florida
    Messages: 34

    here's a pic

    dscf0046.jpg
     
  7. wyldman

    wyldman Member
    Messages: 3,265

    That's a hot air heated choke.You need to check and make sure the heat tube is not broken off or rotted out,and the passages are not plugged.

    You can drill out the rivets,and use small fine thread self tapping screws to replace them.You should be able grind off the small raised section on the cap,so it will rotate.Then turn the choke cap one notch at a time until you find it still starts well,but the choke comes completely off when hot.
     
  8. snowjoker

    snowjoker Senior Member
    Messages: 283

    Chris isn't there a manual conversion for that choke? I thought i seen one but cant remember
     
  9. wyldman

    wyldman Member
    Messages: 3,265

    You can get manual conversion kits,but why bother ? They are cheap plastic,which just gets brittle,as ends up breaking,or the cable siezes up.

    I'd rather have the factory heated choke,or a newer electric style.
     
  10. 79Chevy

    79Chevy Junior Member
    Messages: 29

    wyldman

    "I'd rather have the factory heated choke,or a newer electric style. "

    On that note..... lets say I have an electric choke on my Rochester Q-jet....
    But I have no idea where to plug it in at...

    When I got my truck the guy complained about carb problems... So I rebuilt the carb the best I could (with no knowledge of carbs) but right away I noticed that what I now know as the electric choke was never connected to anything....
    Also when I bought the truck it came with an Edelbrock intake manifold, and the only reason I bring that up is because I was scrolling through a bunch of pictures of 350 engines and saw a wire going from an electric choke down... but couldnt tell where it was going...

    sorry to just butt into the subject...

    thanks anyway...
     
  11. wyldman

    wyldman Member
    Messages: 3,265

    A heated choke requires 12V from an ignition feed.Most GM's also have an oil pressure switch in series with the choke,so it only gets power when the engine is running.