Car stalls during coast/braking

My car has recently been stalling while coasting/braking to a stop. The rmps will begin to jump anywhere from 400 to 1500 while off the accelerator or on the brake. Has been doing this with the MAF disconnected because I had the same problems with it connected. Any ideas?

Car is a GTP 3.8 SC with 75k miles.

Obvious your problem is not the MAF sensor. Check for vacuum leaks since the problem is there only with brakes applied or in closed throttle conditions where engine vacuum should be high. Inspect all vacuum lines at the throttle body and supercharger especially going to the power brake booster and other sensors like the MAP, boost control solenoid, fuel pressure regulator and evaporative emissions system. Also, how are the brakes working?