car keeps shutting off

just bought a project 86 monte. when i start the car its shuts back off so i turned the idle up to about 3grand to keep it running. then next i did was step on the brake and the rpm dropped and picked back up when i let off the brake. then when i braked and put it in gear, the car shut off. but start perfectly fine again. ive heard could be bad vacuum leak or ruptured brake boost diaphram. anyone have any info about this.

1986 monte carlo
350/350 with 2barrel quadrajet carb

No such thing as a 2bbl quad, but yes start by looking for vacuum leaks, then look at carb problems.

No such thing as a 2bbl quad, but yes start by looking for vacuum leaks, then look at carb problems.

thnx, n i meant rochester not quad