1997 Mazda 626 misfire when at normal operating temp

Vehicle runs and drives brilliantly wen cold, once the engine comes up to normal operating temp it creates a misfire under a load at low rpm. Above 2000 rpm there is no misfire and the engine does not struggle at all. If the engine is under a load at low rpm and the throttle is opened all the way it will backfire through the throttle body and air box. Im thinking an electrical component is at fault because of the heat factor and I suspect coil packs as it is a ditributorless motor. The engine light has not come on. Is anybody familier with this problem?