take it to a diagnostician, mechanics will toss parts at it like you have. The fact its happened after you replaced the cat should give you a clue.Thanks so much for the ideas! I originally had a P0420 code, Catalyst System Efficiency Below Threshold pop up and ate the cost of replacing the cat converter. Been suffering poor gas mileage since then! It's been a money pit, but I love this little car! I think I'll take your advice and have a mechanic diagnose it. Thanks again!