I just failed the Ohio echeck cause of the NO emissions levels were too high?

I know high levels of NO is caused by overheating in the chambers. I just noticed that my air filter hose elbow has a small crack and can make the fuel mixture a little lean. I just don't want it to be the egr valve

Any solutions or other causes?

Added (1). I HAVE1995 FORD PROBE. AND THE ENGINE LIGHT IS NOT ON So I don't know WHAT THE PROBLEM COULD BE

Egr valve is cheap. Around $20 in a junkyard. Ask for it to be the egr valve. Easy replace and cheap. You can try allowing more air into the engine by takin off a vacuume hose. Put super unleaded In it also.

NOx is not as hard to control as HC but is harder than CO. There are two major causes of excessive NOx: excessive combustion chamber temperature, which results in more NOx being formed, or excessive free oxygen in the exhaust which prevents the catalytic converter from reducing the CO that is formed. In fact, free oxygen level of just 2% (air is 21% oxygen) will effectively stop the converter from reducing NOx. The full report - levels of each at both speeds - would help clear that up. If CO was suspiciously low when NOx was high you would be looking at why so much oxygen.

We also have no idea about make, model, or year of your car, truck, or moon rover. Some vehicles don't even have EGR, and by the time a vehicle is more than 5 years old the EGR passages (rarely the valve) can be sufficiently choked with carbon to increase NOx. In cars sold after January 1996 EGR blockage should produce a check engine light with code P0401.

I guess really it could be a number of things if you failed because of high NO emissions levels. 1. A lean fuel mixture 2.defective EGR system 3. Maybe even a defective catalytic converter… And yeah like you said engine overheating will cause problems with it a bad radiator, hoses, thermostat things like that could easily be one of the contributing factors to and overheating problem.

You have to go through a proper diagnostic to figure out what's wrong. Guessing never works and leads to expensive parts replacing.