Hi guys. New to the forums but old reading your solutions. This time i need some input. My 2001 996 C2 has a P0448 code (Evaporative Emission Control System Vent Valve/Solenoid Circuit Shorted). Ive already changed every sensor related to the evap system including the tank’s vent valve and even the canister itself. There is no other code but the car still idles and runs like crap. Any help will be appreciated.

 

If you replaced the vent valve and are still getting the code then it's possible that the wires that are shorted, or something's wrong with the computer. This valve won't effect how the car runs so I'm thinking that maybe the problem is that the purge valve is stuck open and the computer is mistakenly pointing toward the vent valve, a stuck purge valve will make it run crappy. The purge valve is the one that allows intake vacuum to flow through the EVAP system. I don't know exactly where in the engine compartment it's mounted. Find it and blow through it to see if it flows air, it should only flow when commanded by the computer, generally during cruising conditions. Sometimes cleaning will cure a stuck valve.