Steve I have read your posts on "closed loop control" and am sorry to say it is way above my head. What is more, where I live it is difficult to find a mechanic you wants to tackle these issues. Even the dealer closest to me does not seem interested in troubleshooting when it means more than reading codes.
However, the issue of the mixture being set too rich and the control system being overwhelmed intrigues me. Why and how could that suddenly happen?