Volvo RWD 200 Forum

Howdy fellow bricksters , Has anybody had the experience of a new o2 sensor not working right out of the box? I am working on a '89 240 (235,000 miles) that is running rich. I checked the old o2 sensor and the voltage was steady at .9v so I put the new one in and it measures the same approx. .9v. While I was attempting to remove the old sensor I broke off the bung nut and then ruined the threads removing what was left of the old o2 sensor. Welded a new nut (leftover tie-rod nut) in placed and installed new sensor. I also had to remove what was left of the old cats guts as it was breaking apart inside. After I clear the CEL (by pulling the 25A fuse the car run and idles great, then I drive a few miles CEL come on and the car returns to the rough idle/running rich condition. I find it hard to believe the new sensor is bad but what else could it be??. Thanks for all the info , past and future :
p.s. clearing the codes at the A/B box does not turn off the CEL, only disconnecting the power works for that. also I seam to remember their was a different way to clear the codes besides the "Bentley way" I had to push the button a number of different ways, something like push button 4 times wait then 5 times wait then 1 then 5 then 1 time, afterwards the led would flash rapidly. That cleared the CEL then. That procedure came from a volvo publication I don't have anymore.

peter