Got labled a gross polluter for failing nitrous oxide emissions. HC was 10-20% of allowable, CO measured 0%, but NO was way high. After failing, did a search on this site and saw recommendatins to get a pre-test. Too late now. The EGR passes all the diagnostics in the GM manual, however, hooked up a vacuum gage to the EGR port so I could read it while driving. The EGR gets vacuum when accelerating but it kicks out during cruise. I guess it kicks out on the smog treadmill test too. No codes show up and timing is set at zero degrees. Any ideas what I should look for next? Would methanol or one of the drug store addatives help reduce Nitrogen emissions? Thanks in advance for any replies.