Originally Posted by lstepnio

I'd put couple bucks on a failed EGT proble or one that kept backing out and was removed. Both situations are very-very-very common. The EGT probe is only there to prevent a total meltdown of the factory uppipe cat. The forced induction Subaru's that don't have an uppipe (2.5L STi, Forester XT, not sure about the LGT) don't have the EGT sensor.

The other good guess is rear O2 sensor "fix", which is common for anyone with an aftermarket exhaust.