The above is a good point.
However, assuming it IS the spark plugs. I am running autolite iridium plugs, they are smooth and great! I know some of you do not like Autolite, but they are the only makers of an iridium plug for our cars. NGK doesn't have a iridium model for the 2.2 (I would've bought that).
Make sure you follow torque specs and use anti-seize grease. All VERY important, also check the gap.
MODS: GMPP "Performance" cat-back, GMPP intake, GMPP extrude honed header, GMPP ground effects kit, lip spoiler, gen 4 headlights, DC sport strut tower brace, splitter, vortex generators, motegi SP10, Iridium spark plugs, ractive aluminum pedals, white carbon shift knob, shorty antenna, 4300K HID low beams (screw electricals warranty)