Well, in that case, maybe the problem is still possibly in the ignition
system.

Did you check the distributor cap for cracks and worn contacts/centre
brush? Maybe you should wait till the car acts up again and then pop
the hood and start tracing back the problem from each system involved -
spark, fuel and air. I suppose the battery is healthy? After the car
has sat for a while, do a quick open-circuit check of the battery.
First remove the surface charge in the battery. Then disconnect the
negative ground cable and test with a digital voltmeter - don't use an
analog meter, I believe it draws too much current to be accurate.
Battery should read 12.4V or better. If your battery is low have it
recharged with a proper battery charger - the car's alternator won't
necessarily do it because it is not designed to recharge a deeply
discharged battery. A battery at 12V may not recharge at all.