What's happening. I have a 2000 Lincoln Ls with Advance Trac. There is a hissing noise coming from my brake booster and my brake pedal has to go all the way down to stop car. I'm also getting a p0171&p0174 code(lean fuel) and stalling. My mechanic said all this is coming from the vaccum leak from the brake booster. He didn't notice any hoses damaged and suggested I need a new brake power booster. So, does anyone have or had this problem. I'm hoping There's something we missed and don't have to replace the brake booster. If so, where can I get one(excluding dealer) because the advance trac model seems impossible to get. Even a used one is seeming challeging.