I have a 350 carburated Chevy Blazer. During the winter when I start it the Truck runs at a very (almost Racing) idle. It doesn’t seem to kick down. When I am sitting at stoplights it feels like the truck is wanting to take off. If I step on the gas at the light the truck almost seems to stall. If I just take my foot off the gas the car will go at about 15 mph without me stepping on the gas. If I ease on the gas it is fine. Any ideas what I could do to fix it.
You can help that situation in a few different ways. One is by adjusting the choke thermostat. Thermostatic spring. It is that round black plastic thing. Drill out the rivets and install sheet metal (self tapping) screws. One at a time. With the screws loose, turn the black cap until the chohe has less spring tension but still closes when cold. You have to push the gas pedal halfway down first to get the choke in the closed position. This could help some. If it’s not enough, look for the fast idle cam on the linkage. It has a screw that rides on it. Back the screw off a half turn and see how that works. That cam will move because it’s connected to the choke. The choke thermostat may already be held in by screws if it has been replaced or adjusted in the past. Remember to reconnect the vacuum line(s) when you put the air cleaner housing back on.
Inoperative choke, hanging fast idle linkage, choke not opening all the way and linkage hanging on the secondary lockout pin if the carb is a Quadrajet and equipped with this could be behind the fast idle problem.
The stalling when you step on the gas could point to a faulty accelerator pump circuit; clog, stuck discharge ball, worn out accelerator pump seal, etc.
Given you have 2 carb problems on an older vehicle I’d say it’s probably time to just overhaul the carburetor and weed out all other potential problems in one shot.