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VW Jetta 2.8 failed smog test for high HC and NOX at 15 mph

My 1997 Jetta failed the smog check for high HC and NO at 15 mph but passed the smog test at 25 mph. My VW has been sitting for 8 to 10 months. Prior to the smog inspection I changed the spark plugs, ignition coil pack and SAI system. Could stale gas have caused my car to fail the test?
Answer:

Stale gas could have been the problem. As well as not enough drive time to "blow out" the Catalytic Converter (CAT) and get it working properly again. We recommend a fresh tank of fuel (1/4 to 3/4 full), and 200 - 300 miles worth of driving prior to your next smog check. Remember your VW's engine is a fuel burning machine. The fuel you use needs to be highly combustible in order to burn thoroughly, or less it will leave behind high amounts of HC and possibly CO. NOx would not be effected directly however we can not assume the cause of the high NOx failure due to the possibility of having stale gas. If your VW Jetta fails for high NOx after getting tested with fresh fuel, we'd suggest looking into a defective Catalytic Converter. Your Jetta is non-EGR valve equipped and the function of lowering NOx falls heavily on the CAT and air/fuel management. posted by SmogTips Support

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