Vacuum leak or brake booster?

[Coach]

Think I have either a vacuum leak or brake booster issue. Truck runs great, but when I come to a stop, the idle drops to about 200RPM and wants to die, then slowly comes back to normal. This only happens when coming to a stop. I have a couple vacuum caps on the carb that look old and cracked, so I'm going to start there. Any thoughts??

[B. W.]

If replacing the vacuum caps doesn't help, clamp off the booster hose ( or remove & plug), then try again. Be aware, the brakes will not work well with the booster unplugged.

[geezer#99]

And what carb you got.
Could be a momentary flooding due to a high or sunk float.

[kcmarkd]

I had some idle weirdness too, and figured that I had a vacuum leak somewhere. I disconnected all vacuum: distributor, choke pull off, brake booster, etc. Truck stopped wanting to die at idle in gear. Then systematically reconnected each vacuum device and found that when the brake booster was reconnected, the symptom reappeared. I verified that the brake booster was the offending party by trying to pull a vacuum from it. No joy, no vacuum.

Ordered and replaced the brake booster. Now it idles in gear like it used to.

[Coach]

Thanks for the replies and advice. The carb is a Holley Street Avenger 670 with electric choke (4 years old).

[hugger6933]

Spray the upper intake and around the carb with carb cleaner and when/if your leak is found your idle will change showing what you need to work on

[Mike_The_Grad]

I have a vacuum leak that is intermittant. It is at the port on the base of the rear of the carburetor. When it's cold it drives great. As it warms up, issues arise. After checking everything I learned that the threaded connection will loosen up as the engine temp rises. And the brake booster hose falls slightly towards the intake manifold and that's when I get a vacuum leak. Troubleshooting is the only way to locate these kind of things. I would heck everything as it is cold and again as it warms up under "normal operating temps and conditions".