Hi everybody
Today my car, a 1992 300TE with 153kmiles failed the MA emission test. The car was put on a dyno and it was run up to 30MPH (it is stated as "transient test").

The values are as follows:
HC grams per mile: 0.98 reading, 1.20 limit -> pass (reading corresponds to about 320 ppm)
CO grams per mile: 006.13 reading, 20.00 limit -> pass (reading corresponds to about 0.6%)
NOx grams per mile: 03.01 reading, 2.50 limit -> fail (reading corresponds to about 1400 ppm)
CO2 grams per mile: 445.99 reading
O2: about 0.5% (as read from print-out graph)

Reading previous posts I understand that high combustion temperature cause high HOX. If I have understood correctly, ignition timing (the later the cooler), EGR function, mixture (lean -> hot), detonation and load can influence the temperature.
In order to find a place with a short line I have been driving around the city for about an hour. The car was quite hot from all the stop and go. It was then sitting about 10 minutes before the guy took it into the shop for the testing. Also, HC is close to the limit too, do I need to be worried about that? And finally, O2 seems a little high as well, pointing to a low efficiency of the converter (not hot enough, broken?).
Many thanks for your input, Bruno

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1992 300TE 160 kmiles