I vote plugs and wires..I had the EXACT same problem and wires fixed the issue.

I did the wires did not help at all

This diagram shows the grounding strap from the battery where it grounds to the body under the rear seat. (#1 in the diagram). The threads on the bolt and on the body get rusty. It is also bolted to a painted surface. Having a similar problem on a 00 SSEi, after cleaning up the bolt and the threads in the body, adding a star type lock-washer under the lug to bite better through the paint, and adding dielectric grease - the problem went away. It has helped some, but not others. Either way, it'* a good preventative maintenance step.

oh ya and plugs and everything else for a tune up