while traveling down a road going about 50mph i started to notice a very slight hissing noise coming from the driver side. I shrugged it off and continued driving. I arrived at a stop light and my car completely died. I was like wtf? so i turn her back over and the hissing noise is now incredibly loud and the engine wont idle at all. Basically, i have to rev up to 2 grand to even get the car to stay on, and when i do this the car is VERY unstable. The PCV pipe is perfectly fine and i dont see any holes/leaks in the pipes. Any ideas? 1966 A code mustang with headers, cam and intake. Just put those on about 100-200 miles ago