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1986 chevy 454 idle issue

Discussion in 'Carb Fuel Systems' started by Lockhart66, Jan 16, 2020.

  1. Lockhart66

    Lockhart66 Junior Member

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    Joined:
    Jul 10, 2019
    Location:
    Washington
    First Name:
    Garrett
    Truck Year:
    1986
    Truck Model:
    K2500
    Engine Size:
    6.5l Detroit diesel
    Hey there guys,

    I just bought this 86 c20. The 454 hasn't been tampered with still has all the smog stuff dual air pumps and all that.

    The issue I am having. The choke seems to work. when I press the gas with the truck off the choke plate snaps closed. When the truck warms up and I give it a big rip it idles down. Then I go to drive it. When I get to my destination and put it in park it idles back up really high. I don't know how high because the truck does not have a tach, but it seems really high. Then when I turn the truck off it backfires like a gunshot.

    I'm a young guy and new to carbs. I have messed with 6.2 diesels but this is my first carbureted square.

    Any help or advice would be super awesome!
     
  2. SirRobyn0

    SirRobyn0 Full Access Member

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    454
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    Joined:
    Dec 6, 2019
    Location:
    In the woods in Western Washington
    First Name:
    Rob
    Truck Year:
    1984
    Truck Model:
    C20
    Engine Size:
    350
    sorry no one responded sooner. first thing I'd check is to make sure the throttle is closing all the way. If it's got an idle kick make sure it retracts when you turn the key off. I'll key watching this thread so post back if you want more advice.
     
  3. bucket

    bucket Super Moderator Staff Member

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    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    It could also be that the choke actually isn't opening all the way and it gets stuck on high idle again.

    When you stop again and the idle is high, have you tried kicking the throttle again to drop the idle like a cold start?
     
  4. SirRobyn0

    SirRobyn0 Full Access Member

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    Joined:
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    First Name:
    Rob
    Truck Year:
    1984
    Truck Model:
    C20
    Engine Size:
    350
    He's got a really good point, and I have run into that before where it seems like a vehicle kicks down off of fast idle fine, but it's really not. It's coming down part way, but because it's still not all the way up to operating temp, it seems like it.
     
  5. bucket

    bucket Super Moderator Staff Member

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    First Name:
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    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    I've had a couple that actually would kick down all the way, but as soon as the throttle was opened again, the idle would step back up.


    I forgot to mention that in the mean time, until the issue is figured out, it would be best to shut the truck off while it's still in gear. That will keep the rpm down and should keep the backfire from happening.
     
    idahovette likes this.

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