1986 chevy 454 idle issue

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Lockhart66

Junior Member
Joined
Jul 10, 2019
Posts
2
Reaction score
0
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!
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,698
Reaction score
11,151
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
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.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,468
Location
Usually not in Ohio
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?
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,698
Reaction score
11,151
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
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?
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.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,468
Location
Usually not in Ohio
First Name
Andy
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.
 

Forum statistics

Threads
41,855
Posts
903,581
Members
33,368
Latest member
TheDuke
Top