Ok well I just wanted to eliminate that since its the simplest and most common. I would do the diagnostic like stated above and see if anything pops up. If it doesn't show anything I would start looking for a vacuum leak.
Diagnostic mode is handy for locating a bad coil, but you have to remember that you're not going to be firing under a wet 13/1 compression outside of a cylinder. That means the spark, on even a bad coil is going to jump massive gaps.
Use an ignition tester that supports a L-A-R-G-E gap. Test each coil on their own wire, then each coil on the same wire. The gap should be narrowed to the point at which it is able to consistently fire without a miss. They should all fire at the same gap. Your anomalous coil is your culprit.