1990 Ford Ranger

I have a 1990 Ford Ranger, and when its running and the brake is pressed, it hisses and the engine revvs. Any ideas why? I've been told its the cadiladic converter or theres a hole in the brake booster. They work fine, other than the hissing and revving.

Check your vacuum lines. Hissing noise could be a vacuum leak. Have someone press the brake with hood open and you out listening. Might be the vacuum booster leaking