Code P0204

P0204 (#4 injector circuit fault) without a P0304 usually means the wiring to the injector has a problem. It is set when the ECU does not see the correct returns from the injector as it fires it. Common causes of the code are a shorted wire to injector four or an open. If you have a NOID light you could connect it and see if there is a good injector pulse to it. No pulse - open circuit. No NOID light? Use a common test light, it should pulse when connected in place of the injector. Next follow the wires (the trigger wire to the ECU being the more likely issue) from the injector back to the ECU. Look for areas the harness rubs or may have been damaged by heat.
The poor running is commonly caused by this code (and the ones for the other injectors) making the system switch to limp mode to protect itself. Once the problem with cylinder four is sorted out it should come out of that on its own.