I have S420 1995 with 223,000. I am not an auto mechanic but pretty good with cars. this car I have for about 5 years. I don't drive it much now so simetimes after sitting for two weeks espasially in a rainy seson it would start good but a few minuts into driving it would start to misfire. sometimes it fills like the engine is chocking untill it gets to 3500 rpms then get power back but if I just push axelerator very lightly it would go very slow but smooth. restarting the car does not help. then after sitting a few hours it is back to normal. then again... I am totally lost between asr system, timing problem, camshaft positioner sensor or just sparkplug wires. It might be loosing contact with one of the sensors ocasionaly but which one? even when engine is not misfiring it feels a little like it is chocking when I am trying to speed up. any one resolved this problem or have any idea please help.