Emissions Fail

Hello
Could someone please help me? I have a 94 accord ex with 250k miles.
This car has always passed its smog checks. Yesterday It failed! The check engine light has been on for a few months and I assumed it was a vacuum leak. I did find a crack in the intake hose leading to the air filter and replaced it. I drove it for a few days and the light came back on.
The smog test failed on the NO (PPM). at 15mph it measured 3109 but at 25 mph it was at 651. so it failed at 15mph? Also I filled the tank up with premium gas and drove it for a week before the test. I checked the vacuum pressure on the EGR valve while it was on the car with a vacuum pump while the car was on and while it was at idle. They both held the presure. I'm Clueless?

Any help? Please