Failed NO Emissions Test

My 95 Firebird failed its emissions test yesterday....blew away all of the individual components other than NO%. Never had any problems passing in the past and appears/sounds to be running well. Any suggestions on what might be the cause here before I submit it to the garage for who knows how many hours of labour!

yer probably goint to have to go to a shop if the engine liht is not cuz u could have bad injectors or cat there is a lot of crap that could couse yer problem

did you have it tested twice? could be a bad test. other than that how are the sparkplugs, wires, egr valve. NOx comes from high heat in the combustion chamber ie, your egr valve isn't opening, or is clogged.

Try buying some synthetic Carb cleaner and cleaning out the Intake manifold and then take the car to a shop that does high pressure fuel system cleaning, If yours on the east coast Mavis or GoodYears do this for about $ 70.00 and you should be set. If its something bigger than this its usually caused by a failed or missing emission's part