I have a 2004 WRX with about 67K on it. Back in the winter the engine light started coming on. When the light comes on the engine loses power and I here some ticking coming from possibly the valves. Sounds like bad gas does. When it does this, I shut the car off and start it back up. The engine light remains on, but the car works fine. If I turn the car on and off about five times or just drive it awhile, turn it off and then start it back up the engine light disappears. I had he computer checked by my friend and it was throwing an O2 code. I brought it to Subaru and they didn't know what was wrong-some master techs they were. They still charged me $90. It really does seem like a sensor because of the randomness that it comes on. Seems to only do this when it is wet or humid out. One time it did this right when I drove over the underbody wash at the carwash. Usually it does it when I am shifting gears and sometimes while cruising on the Interstate. The car is all stock. Any ideas?