Problem with BRAKE BOOSTER or LEAK IN HOSE? PLEASE HELP

I was driving my 1992 pontiac grand am like any other day when I heard a quick clanking noise. I then noticed that when I stepped on the brake pedal a pretty loud hissing noise came out of the brake pedal area. I didn't notice any difference while braking but I did notice that when the car was idle and i stepped on the brake pedal the rpm's went up a little then when I let go it felt like the car wanted to stall. I ruled out the brake master cylinder because the brake pedal regains pressure and it does not go all the way down ( but i could be wrong). I'm assuming that it's the brake booster or a leak in a vacuum hose. If so how can I detect and fix? Can anyone please help, thanks?

Welcome to AF!!

If the vacuum line is bad simply replace it and see what happens. Generally the problem is the one way valve where the line connects to the booster. If the booster were bad you wouldn't have any boost when the brakes are applied.

If you run your hand over the line with the engine running you should feel a suction agianst your hand. Since the line is inexpensive just replace it regardless of what you find.