So I havent gone through all of my vacuum lines and idle control valves, but the truck idles nice almost all the time until I drive it then use my brakes at a light. The idle will drop down to 500 or below sometimes. Once I noticed it was with the brakes, I tested it and pressed in the brake pedal5 or 6 times in a row and each time the idle dropped 10 or 20 rpms.
Any help on this?
Im going to go through brake booster vacuum lines this weekend.

 

Pull a vacuum to the line of the brake booster. It should hold perfect vacuum indefinitely. It sounds like the internal diaphragm of the brake booster is leaking.

 

With the motor off, the brake pedal should get really hard to push after a few presses. Keeping your foot on it and starting the motor, it should release a bit. Check the check valve too

shem

 

Ok, Ill give it a look this weekend. thanks