Hello everyone, I need some help on the brakes on a 2000 mustang V6. I just recently did a brake job on the rear (new calipers, rotors, and pads). We bled the brakes to old school way (one person pumps brakes and then holds, other opens the bleeder screw, etc.) and the pedal still seems to be spongy. I don't know if there is still air in the lines or not. But when i press the brake pedal with the car off, i can hear the brake booster "hiss". And when i press the brake pedal when the car is started, it almost seems to misfire. Could this be a bad brake booster? We are planning a trip down south in a couple days so i need some info before then. Thanks in advance to anyone that helps.