Also, misfire codes can be caused by a stuck closed injector. Often, a stuck injector will recover as the engine warms.
Only know this cause one of my Impala's did it. I hadn't started it in months, fired it up, had a misfire immediatly, misfire code within 30 seconds.
Plug was dry,so I exchanged it with next cyl up. Misfire stayed with first cyl. and did not move w/plug. I let it run abot 10 minutes, and I could hear the cyl. start picking up.
Was fully functional within a minute or two. I cleared codes and threw a bottle of injector cleaner in it.
Concern has not recured since.