Dr.Chill

I have a 2003 A4 3.0. It started with the car not starting one day in a parking lot. It turns, just no start. Towed it home and tried to start again and heard a loud boom and lots of smoke coming from engine bay. Then I saw bits of the PCV valve on top of the engine. Anyone know what could cause the pressure to build and explode that valve? Any advice would greatly be appreciated.