90 240DL

I have a 1990 240DL, I was getting oil into the intake manifold from the crankcase ventilation system. I took the car off the road for one year, then the crankcase ventilation damper was replaced. This remedied the oil in the intake problem, however I now have a new problem. The engine runs rough at idle and is running very rich. (black smoke out of the exhaust) It runs very roughly when it is first started cold. Once it warms up it runs much better, but still has black smoke from the tailpipe. Could this be caused by a faulty sensor somewhere in the system and which one would it be if that is a possibility. Before I took the car off the road, it ran well,and without the black smoke, but had the problem with the oil being forced into the intake manifold.