Hissing Brakes

Whenever I take my foot off the brake, there is a loud hissing sound coming from the area near the pedals. It stops when I push down hard on the brakes, but restarts the second I let up. It started out as an occasional sound, but has become more and more frequent to the point of being non-stop. It has also become louder with time. I am guessing it has something to do with a leak in a hose for the vacuum, which would be cheap to fix right? Could there be something wrong with my master cylinder or my booster (which would be significantly more expensive to repair)?

Sounds like a problem with the brake vacuum booster. It’s not a cheap thing to fix, but it’s something you need to do.

Bad news. Chances are, it is a bad brake booster. If it were a hose, the problem wouldn’t depend on the foot on the pedal. Is the car running OK otherwise? With a leak in the booster, the leak can be big enough to cause rough idle, or an engine that revs up and down.

It does have a rough idle. You are correct. It must be the brake booster.