Hello, how long since a tune-up? Any codes? Can you put a scanner on it, to look at live engine data? As far as ignition, I have used a dmm as a quick test, it's an inductive reading at the plug wires. You don't take the plug wire loose and don't penetrate the insulation, the reading is inductive, you just touch the meter lead to the wire. Compare the readings.
Can you check fuel pressure? You need to test when the problem is ongoing.