I have a 99 Forester, auto, 41k miles. MPG has dropped 10-15% in the past 3 mo. I replaced the plugs and air filter and drove the car 200 mi with no problem. On the return leg of a 130 mi highway trip the plug boot on the #2 cylinder popped off twice. The CEL flashed until I replaced the boot. The 2nd time the CEL stayed constantly on for about 20 mi until I filled the car with gas. After that the CEL was gone. Are these problems connected or separate?

Thanks. I called the dealer and was told that if the CEL was out, the code was gone.

Sounds like an O2 sensor to me. I'm not a mechanic and its easy to access the computer for the engine code so good luck.

-Charles-