My 4th gen prelude just failed this test. According to the results she is spitting out too much HCs, CO and NOx at 15mph. I have a breather on my car, which of course failed visual but that can be fixed. Other than that what else could be the problem? A test to find out runs about 160$!

 

Well, to start out, how many miles does the engine have on it? It could be any number of problems with that vague of a description.

 

Sounds like your converter is not doing it's job, could be slightly clogged. If all three was high it's a converter issue. But getting the car diagnose is the sure way to find what the problem is.