Sure .. it could be the ECU .. or, the harness , or, the coils, or , the OVP , or, an injector, or ... well , you get it now..

What I am trying to tell you is.... IF a 104 engined car with DIS ignition comes in with a misfire complaint, before anything gets done, tested , looked at , etc... an experienced tech changes the connectors under the coils ..
WHY ????? b/c of their known fail rate !!!!!
..,and they should be changed with a plug change anyway... so it is an all gain, no lose situation.

If you want futher testing and more specific diagnosis , build a code reader and go into the ECU fault memory and see which plugs are misfiring, if you even have a misfire ..
But if you want a MOST PROBABLE misfire fault cause on a 104 engine educated guess, it is the coil connectors , hands down .. that's all...
Change them and then you will know or bring the thing in to a Dealer and have it diagnosed .. connectors will cost you $30, a diagnosis will cost you in the Hundreds...with the results probably being "You need new plug connectors, Sir ""