Buy 2 spark plug non foulers from auto zone. Drill one out and attach them together. After that you screw the combo into your O2 bung and your O2 sensor in the other end. It makes it so your O2 sensor is far enough out of the direct exhaust stream so you won't throw a code. It only cost me like $5 and I have never thrown a code. Or you could buy a electrical fix from Mastro or PonyExpress and solder into your O2 sensor wiring. I had this on my last WRX and it worked just as well. It's like $25 though.