Have got a 1998 ml320 with 78K on the clock. It has been recently serviced INCLUDING all 12 plugs !!! Now the b*tch is miss firing at 4K revs and I can not get it past that mark on the rev counter becuase the mssing is so severe - feels like I am only firing on two cylinders. The question is are my "ignition boosters" or coils - shagged - id so how much do the costs and do I need to replace all 6 of them at £110 plus VAT EACH