I have a 98 Nissan Sentra SE. I just took it down for its last emissions test (Colo. Springs is no longer doing these tests after the end of the year due to improved air quality).
Emission test results:
Odometer: 153248 miles Idle 2500 HC PPM 0 0 CO % 0.00 0.00 RPM 806 2382
Catalytic Converter -- Pass Fuel Filler Restrictor -- Pass Oxygen Sensor -- Pass Check Engine Light -- Pass Fuel Cap Results -- Pass
Overall Result: Pass
The only maintenance I've had done on the ignition/emission system, besides what is recommended in the Owner's Manual, was replacing the spark plug wires -- a few years ago, it was starting to run a little bit rough at idle, and I took it down to the shop I usually go and they hooked it up to a scope, and said two of the spark plug wires were bad.
Just thought I'd pass my comments along -- in this day and age, its not too often I get to make positive comments about products.
Everyone have a nice weekend --
Jim