I have an 89 240 wagon with 226,000 mi. I failed massachusetts emissions. The NOx was 7.95 the limit is 3.00. I put a new cat 2 yrs ago. New o2 sensor 1 yr ago. I spliced in a new bosch sensor using the old wiring. It tests ok on a voltmeter- bouncing between 1 and 8 on the scale. So not sure if that's the problem. I recently cleaned the entire air intake system except for breather box which I have never cleaned. My car sometimes stalls when cold and the check engine light will sometimes flash but goes out if I hit the gas. The obd codes are clear 111. I called Ipd and they said 240's are very hard to pass. They really didnt have any useful advice. All I can think of is clogged injectors but dont know if that will produce high nox. I notice water out the tailpipe when cold but seems ok. Any input would be greatly appreciated before I take it to a volvo guy. Did plugs, wires and cap in February. Just put in new coolant temp sensor thought it might be that, but I havent had the emissions tested since doing that. Thanks as always larryb