[updated:LAST EDITED ON 19-Nov-02 AT 10:12 AM (EST)]They do get plugged, but also can go "bad" as it can no longer perform properly and a rotten egg smell is one of the first signs. A bad O2 sensor can cause a funky smell, but that is from the sensor causing the engine to run rich. The smell will be more fuel like(for lack of a better work)