Normally retarding timing, leaning out the screws and increasing idle speed helps,however if you go too lean it will develop a lean misfire which will drive HC through the roof. Need LOTS more info such as..what car,what emisssions equip(AIR,egr,converter?)Remember they made 318's for a long time!What gas failed(or has failed)What other gases are tested?Is it ONLY an idle test or do they check it at 2500 rpm or run it on a dyno?What are the limits allowed? Engine condition?
I can't believe they're still tailpipe testing anything..we dropped it years ago!