Section 254 (Engine Controls - Trouble Shooting - No Codes - 2.2L): Symptoms: Backfires: Sensor/System

WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

Check the air intake system and crankcase for air leaks.
Check the crankcase ventilation system for proper operation.
Use a scan tool to monitor the Knock Sensor (KS) system for excessive spark retard activity.