'87 5000s fails emissions test

[AUDIDUDI@delphi.com]

My '87 5000s failed the new, more stringent Arizona emission test yesterday
and I need some advice as to what might need "fixing" otherwise I will have
to take it to a shop and [gasp!] pay someone else to fix it for me...

Both the HC (.82gm/mile) and CO (5.6gm/mile) were well within spec; only the
NOx reading was too high (6.8gm/mile v. a limit of 3gm/mile).  In the past 4
months, I've replaced the plugs, plug wires, cap & rotor, O2 sensor, cat and
air & fuel filters; I also readjusted the FI mixture and advanced the timing
by 6 degrees. The car runs better than it has in 2 years and gets better gas
mileage to boot but unless I can get it to pass emissions...

Other than resetting the timing to factory specs, I don't know what else to
try.  I know how to deal with HC and CO but have no experience dealing with
NOx and since I only have one free retest (after that, they're $16.75 per!),
I want to "round up the usual suspects" before trying again.  Help!

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                /| |_| |> | - |> |_| |> |  (AudiDudi@delphi.com) 
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               aka Jeff Goggin                     Scottsdale, AZ