A couple of occassions now i've noticed my car only firing on 3 cylinders, usually not for more than a couple of seconds every couple of weeks maybe. I just started her up today (first time since last friday) and she was horribly misfiring along the motorway with the engine both cold and warm. As I came off the motorway she was ok again and rocketed along at full power. The idle has been a little lumpy for a while but mainly when running cold. I have no warning lights on and the car hasnt been modded and like I say, when the car is running fine there's no loss of power at all and the turbo is winding up fine. Any ideas before I change HT leads and check plugs? Cheers. Ben.