[johnsjmc]

NOx appears high and CO as previously mentioned. NOx is caused by high temp /pressure combustion.The usual strategy to control NOx is retarded timing and exhaust gas recirculation before the Catalyst further reduces it. Is your gas stale?Stale gas will allow inaudable detonation which sends NOx up. Was the test immediately after storage? If so retest with fresh premium pump gas.If fresh gas was in use then the O2 sensor could explain the high CO reading but not usually the NOx Have you altered the base timing?It should be set at the recommended point on the tune up sticker under the hood.