Sensor/System Checks

WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

Check the Knock System (KS) for excessive spark retard. See KNOCK SENSOR under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 4.0L AURORA article.
Check the Exhaust Gas Recirculation (EGR) system for proper operation. See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTS - 4.0L AURORA article.
Check for a dirty or damaged air cleaner element.
Check for collapsed, or damaged intake air ducting.