B2200 Emissions Problem...

Hello everyone!

        I was hoping someone might be able to give me some ideas as to what 
might be causing an emissions problem I seem to have.  The vehicle is a 
1990 Mazda B2200 with Fuel Injection in California.

        The CO and HC emissions are incredibly low, almost non-existant, 
which is great, but the NOx emissions are incredibly high, nearly twice 
the max limits.  Any ideas as to what I should be looking for or how to 
fix this problem would be very appreciated.  Thanks!

--Douglas