NOx emmissions ?

[Vikram Mittal <mittalv@yahoo.com>]

My 1990 Audi 100 (fuel injected 2.3l I5) failed the NOx emmissions with
a reading of 1333ppm under load emmissions testing.

I replaced the oxygen sensor (Bosch 3-wire) and the NOx dropped to 1015
which is just under the limit of around 1095 and so it passed.

My questions is, is the current NOx still too high.  The car has 147K
on it and original cat.  The spark plugs and air filter have been
changed recently.

The engine never surges, hesitates or seems to lose power. 

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