here's the story. there is obviously something going on with my "mix". when I bought the 1990 300E it did not pass inspection by .54 on the NOx reading, and the mechanic said to put some fuel injector cleaner into the gas and drive around then come back. Well I did that and now the NOx is fine but the CO went thru the roof!! 76.63!! what do I do. could it be the testers that are at the shop reading it wrong?? I doubt it ... but what are the options or steps that should be taken to fix the problem. does it have to do with fuel injection, the engine, of the exhaust? need help I only have until the end of the month before the inspection dates are expired.