I understand that a rich running engine will idle rough. If one of the fuel injector plungers is worn and some gas is getting by when it shouldn't I think that might cause the rough idle. It is especially bad when very cold outside. By the time the engine is hot, the idle is pretty smooth except fot he occassional little bit that you can barely notice. I would also like to consider other causes. I have done searches and come across something called a cold start, and also over voltage relay. Could someone explain to me what these are, how a malfuntcion in one of them might affect the car, and what are the possible fixes. I I checked the hoses and they look OK.
1995 E420 - retired
1986 420SEL - retired