Sorry this post is a bit long but I would really appreciate some help with an engine problem. Its a 1.8 Vectra Club of 2003 vintage. 77,000 on the clock and regularly serviced. Over the past year have replaced the EGR, Front Cat together with O2 Sensor and Cam Sensor. Serviced 2 months ago with new air filter, GM part synthetic oil and filter, I tend to do the oil at least once a year if not sooner, left the plugs as they were only 6 months old, Bosch Super 4's. Recently getting P0420 Catalyst System Efficiency Below Threshold (Bank 1) Clear the code and O.K. for a week and its back. She is holding back, like a hesitation when puling away as if missing a couple of beats then picks up with a jerk. Also had a code the other day saying rich mixture? Otherwise engine is really smmoth and quiet.
Suggestions please.
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