Hey all,<p>In the lovely county I live in, we have emissions testing for cars that are under 25 years old. Bottom line: this is revenue generation for the county and a way to get older cars off the road (not htat they're going to help me pay for a newer one!).<p>I have a 1991 240 sedan automatic, with 206K miles on the clock. It runs beautifully, but last year, I barely passed the NOX part of the emissions test by three points.<p>This past year, I have relegated my beloved 240 to third car status and it does not get the daily grind commute. I am betting since its not getting driven as much, this car will probably not pass emissions testing this year.<p>Does anybody have any experience in diagnosing what causes high NOX on emission testing?<p>I hate to go in and start replacing the cat and 02 sensor and other things not knowing exactly what causes high NOX...that seems wasteful.<p>Anybody have any suggestions as to what to do, proir to emission testing? I really want to pass and not be out of inspection or have to wind up ditching the car, only because it does not pass their one silly test. It runs great.<p>Thanks in advanc for the advice.<p>- Brickboy240<p>PS - if I have to replace the cat converter (a very real possibility, because I still have the original unit in this 91 240)...where can I find a quality unit for cheap?