I have a 03 civic EX with codes for both o2 sensors and catalyst inefficiency. Sometimes the car will lose power and slowly drop to 200RPM and then after that it will slowly pick up and start to drive normal again. Sometimes it just bucks around. doubt both o2 sensors would be going bad at the same time so I am leaning towards a clogged cat. However the car will run fine for days with out an issue, wouldn't a clogged cat have issues all the time? I haven't had the car long enough to keep track of MPG etc. It has 114k on it. I bought it last week.