can any one help, my 300 sl is playing up, it starts first go sweet as a nut, drive it for about 3 mile then it starts missing and only just runs, by the time you have got it back home, another 3 mile'ish, its all right again. first time it did it, thought it was just cos its been stood for 12 months, but this is the 3rd time same thing !!!!!!! HELP.