I had a similar problem with a 89 740 with 85K miles; runs rough, light goes on, codes point to sensor, problem clears and then reoccurs. A dealer test on the sensor showed it was functioning OK but "lazy"...translate it sometimes doesn't work. Dealer price to replace is $300++; I am inclined to replace it myself. Check the Bosch web site; there is a detailed discussion of sensors there, including replacement instructions. Price for the part about $120 at FCP Groton. I am no genius at this sort of thing, and consider my most elaborate job to be replacing a water pump on a Chevy.