Here is the general process on 104 waste spark ignition misfires ..
You can go in and get the codes for misfire and you can use a scope , etc..
But , the easy way is to first check for a visually falling apart wire harness ,, if that looks half-way decent , pull the 3 coils and change the 3 plug connectors .. they are so cheap and infamously known to cause misfires on 104s , that it is common pratice with Techs to just change them and see where you stand with new ones before wasting a lot of diagnositic time and part chasing... second notorious 104 misfire is the use of plugs other than Bosch F8DC4 copper plugs .. so , do them at the same time .. again, Bosch's cheapo plugs.