How much is the cost to replace the power brake booster?

Thank you cadieman. No hissing noise and when the car is stopped and idling there it does not shut off if you press the brakes. It's only when we are driving it and hit the brakes that it immediately shuts off. I thought it was the strangest thing also. I know a little about cars, and I have never seen this problem. Someone said the power brake booster. I also thought it was electrical, but everyone keeps saying the power brake booster. What do you think?

Thanks KHL0w2008. Negative to both the MIL and I have not checked the codes. I am in Warszawa, Poland right now and it's actually my girlfriends car. But she is really sad and I want to help her out. I will have to hook up the computer to check for the codes I guess. I would think it's an idling speed problem also, but it does not shut off when you are stopped or driving. The idle is perfect. It's only when your driving and press the brake, it automatically shuts off. Everyone keeps telling me the brake booster diagphram and the vacuem is sucking to much air and messing up the air/fuel ratio causing it to stall out. Initially I thought it was an electrical problem.

You know, my girlfriend told me that the whole problem started when she tried to hit the alarm button and open the door. She said it wouldn't open and when it finally did, the radio than wouldn't go on and than this whole thing with it shutting off when she pressed the brake started. I thought maybe the stoplight switch was causing a short, but the brake lights work fine and I checked the battery and its fine. Than I figured its a short somewhere. All this initially led me to believe it's an electrical problem. But than of course everyone started with the brake booster. Im glad you are also thinking it's electrical. I keep thinking it's also electrical. I will do as you suggested and check the wiring.

Thanks for the reply KHLlow2008. No, I checked this also and when the car is stationary and you press the break, nothing happens. It does not shut off or the engine become erratic. It is only with hard braking when we are moving. And the last two days, I tested the car and everything is fine and back to normal. But I don't trust it.

Thank you guys. By the way, I am in Warszawa, Poland right now and its my girlfriends car. So greetings from Poland. I knew I could count on some good old American help. You all seem to have helped me identify that it is definitely an electrical problem and simple. If it was the brake booster, I would doubt that it would be intermittent. Yeah, I played around with the battery cables and that is when this seemed to have stopped. I will look at them again and tighten down the bolts. I will also run the codes KHL. Thanks again-

Thanks caddieman-