Engine is at high idle but when I press the brake in gear the engine wants to die

[Scarlett77camaro]

Hey guys so I just rebuilt the top end on my 1977 camaro with the 4.1 250 inline 6. I can’t seem to get the engine tuned right though. Seems like I have a high idle when in P or N but when I put into gear it runs pretty good. Problem is though when I press the brake hard enough it wants to kill the engine. Also to come to a complete stop I have to basically stand on the brakes. Just got new front rotors calipers and pads and just loosened the drum brakes just a bit but still need to stand on the brakes. Honestly at this point I’m at my wits end. Would love some help!!

 

[Turbo4whl]

Leaking vacuum brake booster would give those symptoms. If the diaphragm in the booster has a crack, you would not have the vacuum leak until you apply the brakes.

 

[RustyPile]

Back to basics.. Base timing is a critical adjustment.. Also curb idle, choke adjustment, and idle mixture adjustment.. If the choke doesn't fully release after engine warm-up, fast idle cam will hold the idle speed too high. Hard brake pedal is indicative of a bad power brake booster..