Before you do anything else, check your vacuum hoses.
I had a code for "bank 1 rich" and found a little rubber elbow
on the intake manifold behind the power steering pump to be totally
deteriorated. Replaced it and the Check Engine light went
out by itself two days later, not to come back (It has now been two
months, touch wood). My car is an 850R 96 model with 115.000 miles
and all O2 sensors are original. I get about 22mpg avg.
Hope this helps.
Thomas