Possible Causes & Corrections

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

Check the following items:

Using scan tool, check for misfiring cylinder.
Secondary voltage components for arcing (module/boots).
Spark plugs for cracks, broken insulator or improper gap.
Spark plug boots for chafes or cuts.
Perform injector balance test to check for clogged injector(s). See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 2.2L & 3.0L VUE article.
Proper valve timing (timing belt), broken valve springs or sticking valves. Perform compression test.