[ozi jim]

MMM.

ECU s generally have over voltage regulators, and it will throw a code.
Depending on the age as to the sophistication of the fault software,it maybe to old for missfire history.
disconnect a plug lead and see if it throws a code in.
Hint If it has no code you look for something that does not log.
EG rotor button
fuel pump
plug leads
What it will log is things like AFM, TPS, crank cam sensors bla bla bla.
It wont log if its not in the soft ware, so induce a fault by pulling a lead and that will tell you if it should or should not log a code on a secondary ign missfire.

If it where me, I would go for a drive and take an inductive timing light with you.

When it starts to miss put the pickup onto one lead at a time and look at the flashing light.,
If one is not firing it is related to that cylinder, then go on from there.
If it is all then move it to the coil lead, if this is ok then it is the rotor button.
To test a rotor, pull the cap off, pull the coil lead out of the cap and hold it about an inch or so above the rotor button, get some one to crank, if the spark is bright and jumps onto the button and goes to ground through the shaft it needs replacing.

One other thing if it has an ignition module put the timing light on the coil lead and then load it or put it into D, if the timing light goes out and the car stalls it will most likely be the ign module.

I am a mechanic, if it is running as poor as you say then you need to gather evidence see if it is all or one.

Jim