First, PLUG THE INJECTOR BACK IN. Circut open 90% of the time means the plug is disconected, broken wire at the plug, or the injector is actually bad. THEN...
Change the plugs and wires anyway, so YOU know they are good. Also if the EGR is stuck open it will cause a P0300 code, random multiple cylender misfire due to a vacume leak, but save that for last.
If it still missfires, unplug each wire at each prong on the coil packs while the cars running to see which one isnt sparking (would be a good idea to use a pair of insulated pliers)
