Misfire Help

hi guys im looking for some help, so i have a really bad misfire which started a few weeks ago, iv'e plugged in the code reader and comes up with misfire cylinder 2, so i cleaned the MAF sensor, put in brand new plugs and changed the coil pack on that cylinder but it's made no difference, iv'e taken it to the garage today and the only advice they could give me was to change all the coil packs and see if that helps, should i do that or is there something i could look at cheers, impreza wrx 2003