noX arent created until cylinder combustion chamber temps reach 2500 degrees fahrenheit. if you have no thermostat or its stuck open then the car would run cooler and richer and would create more HC's.

you are not running rich bc co is down and co is a rich indicator. this is why i asked for your o2 and co2 reading. it will tell you if you are running lean or at stoichiometric ratio. you can also run lean and up with low nox bc if its gets too lean then you will get a lean missfire and you will not have complete combustion. this obviously isnt the case bc ur hc is low. you can still run lean though...thats why we need to know the o2 and co2

everyone did have good ieads about the egr and cat and too adcaned ignition timing, but we need to see what the other readings are before we can decide what it is bc its all speculation and assuming only makes an ass out of u and me