My gas mileage is steadily dropping and my OBD II code is PO442. I bought a new gas cap at NAPA, but that did NOT solve the problem. Where else should I look for leaks that might set off this code? Should I just go to a Saab specialist and get a "smoke test" and save myself a lot of headaches and money by having them replace parts in the system? If I pay for a smoke test, would you folks recommend that I buy and replace the parts myself?