Intermittent problems are always the hardest to find.

I thought of another possible cause of your problems. I'm not familiar with the 2.3 engine but I suspect it uses a hall switch that could be going bad. It is part of the ignition primary circuit and would cause the problems you describe. Hall switches have also been known to fail when they warm up so if your car is running okay in the cold the hall switch is worth checking out.

-John