Originally posted by ChinaClipper
Took the car in for biannual emmissions. Slightly higher CO, HC than 2 years ago, seemed to be running rich.Passed OK
So what was it 2 years ago? Slightly higher to me is about 20%, whats your definition? Its either rich or it's not.
I speculate that your cat is just not as efficient as it was 2 years ago and the higher readings have nothing to do with the A/F control. How many miles have you driven in thes past 2 years? How old is the cat?