Hello. Engine misfires can be caused by a wide variety of issues. If you have already replaced the coil and plug for that cylinder then the next thing I would look at is the injector. If the cylinder 4 injector malfunctions or gets dirty it may not be providing the correct amount of fuel for the vehicle, resulting in a misfire. A vacuum leak can also cause a misfire if a bad hose or gasket allows unmetered air into that cylinder. Another, more serious, but lesson common, potential cause is mechanical issues. If there is an issue with the cylinder 4 valve train components, such as a burned valve or broken spring, it may result in a misfire at that cylinder. These sorts of problems are more serious in nature and usually require engine disassembly to repair. I would recommend having a professional technician, such as one from YourMechanic, come to your location to diagnose the cause of your cylinder specific misfire.