Hi,
This is the same situation I had the last time I went for
inspection... Nox on my 91 BMW 318i failed. Only this time, it has
doubled from the accepted level!  My car an E30 318i with the M42
1.8L
engine was designed without an EGR or any other sort of NOx control,
except, i suppose for the catalyst in the cat converter.

Background:
For reference, in 2003, my emissions (dyno test) were as follows:
NOx 1114 (standard is 1134)
HC 97 (standard is 146)
CO% 0.33 (standard is 0.82)
CO2% 14.1
O2% 0.2

Failure in 2005:
NOx 1167
HC 96
CO% 0.35
CO2% 15.3
O2% 0.3

Replaced cat converter, reading that passed in 2005:
NOx 1074
HC 133
CO% 0.34
CO% 14.8
O% 0.2

My failure today:
NOx: 2126 (DOUBLED!!!!)
HC:161
CO%:0.54
CO2%:14.1

As a reference, my 98 Chevy truck (owned since new) had these results
on its last dyno test (currently exempted because its an OBDII
vehicle, so these are a little old, but done on the same system):
NOx 16
HC 7
CO% 0.01
CO2% 15.2
O2% 0

Spark plugs are very clean and correctly gapped, etc., I even ran the
new Amsoil PI through the tank just before to ensure that CCs, etc.
were cleaned out. No dice.

I do have a dinan chip, Ill be removing it as of right now, to
hopefully be able to pass... The car runs great and gets me good fuel
economy, Id hate to have to spend $500 on senseless repairs to get a
waiver, just because this car never came with an EGR from the factory
(by design).

UGH!

Any thoughts or comments would be most appreciated.  I have heard
that
ingnition coils (this car has a distributorless system) going bad can
cause funny problems like this.  Any thoughts???

Thanks,

JMH