Welcome to the wonderful world of the Delphi "Ion Sense" ignition system. Here a link if you would like to learn more:
http://www.delphi.com/news/pressRele...r1770-04182001
The bottom line is that this ignition system is VERY touchy with plug types. There are only a couple different kinds most people use, and you are best off just getting them from a dealer if you don't know much about cars. You either need to do that, or get the correct Denso's or NGK brand plugs. I don't know the part #'s, so hopefully someone else can help you out with that. Good luck. This may or may not be your problem, just letting you know on the plug thing. Check the intake manifold gasket with some carb cleaner.