I decided to stop pulling my hair out over a low rpm stalling problem and take my car to the dealer. They said that my brake booster was bad and I had a short in the throttle position sensor circuit. The hair-pulling part is that I replaced both parts trying to cure the problem before giving up. I replaced the throttle position sensor and didn't even consider a short in the circuit. I bought the brake booster used and apparently swapped a bad one for a bad one. I knew the old booster was bad because I could hear hissing when I pressed the brakes hard at a stop. When I took it out, you could move the plunger in and out and hear the leaking bladder. But I currently don't have any symptoms except bad brake pedal feel (feels like air in the line) and the aforementioned stalling which I thought was unrelated. Before I installed it, I checked to see if moving the plunger would pressurize the booster. After installing, I noticed when removing the vacuum line that there was significant vacuum at the booster.

My questions are these: How do you test a brake booster to tell if it is bad? Is the brake booster in an ABS car the same as the one in a nonABS car? (I have an 89 760 Turbo with ABS.)

Thanks for your help.