My girlfriend has a 93 Nissan sentra. Its the automatic dohc model. Anyways, today she was driving to work and started to hear a loud hissing noise. Then the car pretty much wouldn't go any faster than like 50 and it stulled on her. So I took the car for a drive and I could hear a fairly loud hissing , or almost a noise that sounds like a huge vacuum leak, coming from not the motor, but actually just infront of the drivers seat somewhere near the transmision. If anyone has any ideas or opinions towards this,, all your help would be appreciated.