i get code P0304 misfire cyc 4 and check engin lite only comes on when coldstart

What is your question?

had co and plugs changed.. lite still comes on when cold and have ruff idle even when warm notice alittle dark spot on coil near plug #4 wondered maybe thats it and sometimes it,the lite will go off on restart when warm...thinking of getting one of those spark testers for deep plugs?any ideas?