I have a 2000 S320 Petrol. It's been sat parked down the side for house for the last 12 weeks only moved every two or three weeks for a quick wash and let it idle for 30mins. I have done this often over the six years when I am not using it but this time it misfires (sounds like it is hitting the rev limiter)I think. When I rev the engine to over 4000 rpm it starts to misfire. but when the car is driven it will not misfire and change gear at the red line. Drove 40 miles today and it drivers just fine but still if rev in park to over 4000 rpm it misfire. A bit long winded but I think that explains it any thoughts would be of help.