Idles high when cold...

[Buzzman]

Hey there,

Tackling things one at a time here with my new '79. Next up is the high idle problem I'm having when the motor's cold. Every morning when I go start up the truck and let it warm up a little, it idles way too high - I'm guessing 1500rms or so. All the way to work I barely have to give it any gas, it just gets up and goes on it's own. And when I turn it off, it diesels for a few seconds and sputters out. Now, when I start it up for lunch, it's usually fine, and idles normal. The rest of the day is fine as well.

I've done a little research around here, but most of the threads seem to be dealing with a constant high idle, whereas mine settles down as the day goes on.

So I know I need to be mindful of vacuum leaks, but because of the dieseling and eventual leveling out, it must be the carb. Could the butterfly valves stick open when cold, letting too much fuel in and causing the dieseling? Or is the problem with the fast idle cam? The only reason I don't think it's the fast idle is because it seem like that would cause it to run high all day.

If it is the butterflies, any tips? Thanks!

[brianthelion02]

What kind of carb is it? It will have a high idle speed adjustment,also check youre choke t-stat!

[Buzzman]

Ah, that would help! It's the stock Q-Jet.

[bmchevy1979]

here you go this is how you adjust it this is the passenger side of carb and the screw might be hard to see for the choke mechanism but it is there

[camshaftgsxr]

the dieseling is most likely just idling too high, mine used to diesel at only 800 rpms

[tucsonjwt]

The choke valve should be straight vertical when the engine is warm. Remove the air cleaner lid when the engine is warm with the engine idling and see if the choke valve(butterfly valve) is all the way open. If it is not, then you can adjust the choke until it is vertical. I converted all my squares to manual chokes (easy $12 fix) because I never had an automatic choke work properly.

[Buzzman]

Thanks for all the helpful replies. I'll check the choke valve at lunch and see what I see. Otherwise, it sounds like the fast idle is set too high and doesn't disengage when the engine is warmed up.

[Buzzman]

So in doing a little more research today at work, I think I might just need to clean it up a little. The fact that it's been getting stuck off and on makes me think that the linkages could just be sticking. It's been getting hotter up here finally and maybe it's getting gunked up. Hoping a little carb cleaner when the motor cools down will help.

[motornut]

Originally Posted by Buzzman

Thanks for all the helpful replies. I'll check the choke valve at lunch and see what I see. Otherwise, it sounds like the fast idle is set too high and doesn't disengage when the engine is warmed up.

if it dosn't disengage then the four barrels won't kick in if it's a stock setup

that little stick will stop it from working the 4 barrels
i bend that so i don't have to wait
this pic of a truck someone bought on here and the choke was tied off