Re: EF RPS High, Hissy Brakes
To check if the brake booster is working OK and that it's getting adequate vacuum and that there are no leaks, do this. With the engine off, pump the brakes a few times to exhaust any vacuum from the booster. (The boosters hold a bit of vacuum for emergency braking if the engine stops while driving). After you've done this the pedal should become quite hard. Then, while holding your foot firmly on the brake pedal, start the engine. Your foot should slowly sink a bit and then stop. If it does this, the booster is probably OK. If you have a continuous hissing sound, there is most likely a vacuum leak somewhere. Get a piece of plastic hose, put one end to your ear and go looking for a leak with the other end around the brake booster hose and fittings. You'll find it! And a leak WILL trash your idle!