Additional Checks

WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.

Check the exhaust system for possible restrictions:

See EXHAUST RESTRICTION under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
Check the exhaust system for damaged or collapsed pipes.
Check the mufflers for heat distress or possible internal failure.
Check for possible catalytic converter restrictions by testing the exhaust system back pressure.
An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a condition exists, check the routing of secondary ignition wires, high voltage components, e.g. near ignition control circuits.
Check for intake and exhaust manifold passages for casting flash.