If the O2 sensor is not over 30,000 miles and has not been contaminated by leaded gas or silicone it does not change all that much. This is exactly the reason the EPA required a lambda counter so that over the lifetime of the sensor it would be in calibration. Other conditions will change much more like the ignition wires arcing or the spark plug gap increasing or a vacuum leak. I would not touch an O2 sensor unless you cannot get the lambda to pulsate within specs (35-45 degrees with CO properly adjusted) or it has over 30,000 miles on it. I bet the sensor will last a lot longer but the EPA in their infinite wisedom probably conservitevly rated it. BTW when you touch anything emmision related (like an O2 sensor) you are supposed to reset the mixture using an analyzer and in some states this can only be done by someone that the state has certified. David Teitelbaum vin 10757 -- In dmcnews@xxxx, dherv10@xxxx wrote: > Dick, Most common, As the 02 sensor gets old, the voltage changes going to the Lambda ECU, the air / fuel mixture will change. Then the 02 will try to adjust which causing it to seek along with a few other things like Dave mentioned. After it warms up, you can adjust the air flow meter to smooth out as long as there are no other problems. If the 02 sensor is new, then you have to re adjust the air flow meter to the new conditions. The computers in the cars today do it automatically. Untill the De Lorean gets a highter level of computer, it's a 3mm long allen ever so often. > John Hervey > www.specialTauto.com