does it missfire when engine revved up or only at idle, have you removed coil pack and connected a plug to each lead and cranked engine to see if there is a spark? have you checked plugs for damaged electrodes? is fuel reaching the cylinders (faulty injector)? has a cylinder compression test been done? whats the coolant level, if its low where has the coolant gone? if its getting into a cylinder it will cause it to missfire when idling. these are just a few ideas good luck
RM
March 2013