How did I fail Emissions?

Okay so I've failed emissions on my stock ass 91 automatic crx dx. I've replaced the plugs within 10,000 miles and wires. I run fuel system treatment monthly. My mechanic said I passed @ idle but I failed @ 2500 rpm. What do I need to do to get it to pass? Oh, he said it wasnt an o2 sensor either.

HELP!

when he put the revs at 2500 were you standing there watching? If you were did you smell a kinda fuel smell. only thing i can think of is it was running rich. you should be able to see how close you were on your inspection sheet if it was really close then talk to the inspector to see whatyou can do to bring it down.

you can try replacing the cat,,,fresh oil change and make sure the car is warmed up plenty when takin the test again,,,drive it for a good 30 min before test