thanks for both of your replies. Before the check light came on both times in the damp/rainy weather the car was difficult to start. It sputtered and chugged, then ended up with the check engine light on and the car stayed on chugging for a bit then settled into what I have now, a car that starts OK but runs a bit rough. So my A/F minimum is definetely a current problem, AND I'll have the dealer check the electrical system.
Thanks!