It has been a couple of months now that I've been getting poor mileage in my '93 850... about 2/3 of normal. I've changed the spark plugs and the air filter, but it didn't change much. I have had problems in the past with the O2 sensor where the check engine light would come on in very cold weather. However, there are no codes in the OBD. I'm thinking of changing out the sensor, just to see, but I'd like to be sure it's needed before dropping the cash. Any thoughts would be appreciated.