Galant 2.4 missing

:banghead: i did a tune up because i was getting a miss on cylinder 3 did the tune up still missing so i swapped the coils around and the miss went away for a couple hundred miles then all the sudden its missing again but on cylinder 4 now i dont know what it is? still runs good but the service light is on can really feel the miss when it is cold i live in ne ohio so it gets cold