1986 GMC C1500 High idle

DAVID1924

MEMBER
1986 GMC C1500
5.0L
V8
2WD
AUTOMATIC
802,117 MILES

I put a 350ci engine from a 1986 blazer in a 1986 (11/1985) 2 wheel drive heavy half. I have a high idle problem, think it's the carborator. We set the fuel level right, put two strong idle springs for the throttle, we set the choke at it's best and yet the choke flap opens just a little then the idle rises and stays high. What else can be done? I'm baffled.

Monday, November 23rd, 2015 AT 7:33 PM

1 Reply

CARADIODOC

MECHANIC
34,330 POSTS

Hold the choke open, then bump the throttle to see if the fast idle cam drops down. If it does, either the choke pull-off linkage is adjusted too long, or the "stove" isn't heating the choke's thermostatic coil. If you have a black plastic disc on the side of the carburetor, there's three screws that can be loosened so it can be rotated to adjust it. There's also going to be a small tube to carry hot exhaust gases to that coil to warm it up. Be sure that isn't rusted off.

Some newer choke pull-offs have a wire connected to the side of that plastic disc. Those have an electric heating element to warm the coil. Check if there's 12 volts there when the engine is running. I'd have to look at a wiring diagram to refresh my memory, but that 12 volts might come from the generator so it doesn't appear there unless the engine is running.

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Monday, November 23rd, 2015 AT 8:38 PM