Toyota Repair: EGR valve, nox emissions, toypta

Question
I own a 1993 Toypta Corolla LE and recently failed one part of an emission test.  It was the NO or nitrogen oxide portion of the test.  I failed approx. by about 250 points.  I was told that it could be my timing, the EGR valve or the catalytic converter.  One mechanic told me that he could not find where my EGR valve was on my vehicle and proceeded to tell me that I did not have one on my vehicle.  I would like to know why my vehicle possibly did not pass emissions.  The check engine light is NOT on.

Answer
you may not have an egr,some models dont.In that case, the engine uses fuel trim to lower the combustion chamber temp to reduce NOX emissions.
Make sure it has recent Tune up, air filter , plugs, change the oil.
Youll either need a Cat Converter or an o2 sensor, The o2 sensor can be "lazy" and check fine.
Start with the sensor, its $100 or so, the cat is several hundred.

Mike