I'll get right to the point.

98 Accord LX 4cyl.

Timeline of events...

9/2005 - Check engine light came on - scanned - DTC p0420, catalyst below threshhold. I told the technician that I really had no money for a new converter. He told me not to worry about it right away, unless my car was experiencing some symptoms. He didn't clear the code.

9/2005-1/2006 - check engine light remained on without any symptoms.

1/15/2006 - car begins to ride rough during first 10min of driving after cold start in the morning. During that first ten minutes, car "wants" to stall when accelerating. Drives fine for the rest of the day. This goes on for about a week.

1/24/2006 - Decided it was time to spend some cash and address the problem. Technician scanned DTC code and got a p1491, EGR valve lift insufficiency. But NO p0420. As a matter of fact, the technician said that the converter seems to be operating fine (after an infrared sensor test). EGR valve was removed, cleaned thoroughly, and reinstalled. Car still struggled, so EGR valve was replaced with a new one. DTC codes were cleared.

1/25-1/26/2006 - car starts and runs fine.

1/27/2006 - engine light come on - scanned - DTC p0401, insufficient EGR flow AND p0420, catalyst below threshhold. No repairs made.

Does anyone know what could be causing these EGR codes? Also, what could be causing the p0420 code, since a mechanic ran a test on the converter and said that it checked out? I was told that it could be a bad oxygen sensor, but isn't there a seperate DTC for that? Thanks guys.