GRRR!!!!

My 940 just failed California emissions. Interestingly enough, the 940 is identified as a high emitter profile vehicle by the state. I realize that one solution is to move somewhere else (and I'm more tempted than you think, despite being a native) but ntil then I have to drive and register the car.

As you'll see from the info below, it doesn't seem to me to be a clear-cut case to diagnose. Everything passes at 25 mph, but NOx fails at 15 and HC is borderline at 15 and 25 mph. I've run a search and read the FAQ but also wanted to appeal to the experts and ask for best recommendations before I go replacing expensive components.


To wit:
1994 944 NA Bosch
140,000 miles
original catalytic converter
original O2 sensor
Car warmed up before test (over 30 min. driving on highway, <5 minutes parked awaiting test)

Test data: (all pollutants are listed Max allowed / Average / My measurement)

15 mph test @ 1876 RPM
HC(ppm): 85/21/78 (marginal)
CO(%): 0.50/0.06/0.30 (okay)
NO(ppm): 695/150/916 (the reason I failed)

25 mph test @ 1875 RPM
HC(ppm): 50/13/50 (too close for comfort)
CO(%): 0.47/0.05/0.22 (okay)
NO(ppm): 717/136/672 (the reason I failed)

I think I should have changed the oil before the test, which I understand will likley take care of my HC.

As for the NOx...is it time to replace the cat and O2 sensor? I'll do an inspection of the vacuum lines and intake side before I go pulling those components.

Thanks for your help!
Matt