I got a 91 mustang and since I bought the car its had a hissing sound when i hit the brakes.(at idle when i put my foot on the brake the rpms would go up) so I just put v8 brakes on it last week and tonight I was driving and I went to hit the brakesa and the pedal got super firm and as i continued to press the brakes harder cause the ebrake doesnt work I thought to my self maybe ill fix the ebrake tomorrow if i get this thing to stop lol...no no back to what happened I hit the brakes and as it was slowing down slowly the car died and now it wont start up. Is this the brake booster or something else?