94' 940 rough idle/cold start
 

A few weeks ago my 94' 940 non-turbo was not starting at all in the cold. We had it in the shop, with the following being replaced.
- Crank position sensor
-O2 sensor
-Water pump
-Battery

As of recently, it has had trouble starting in the cold (-20), was very rough and would soon die. In one case, we let the car sit assuming it was flooded. Before starting again, we checked the spark plugs which were very dirty. Cleaned the plugs, then it started up fine.

While this problem only occurs on the coldest of days, during its first morning starts, I have noticed the car's seems to be idling rough even when warmed up. Just listening to the idle, it is not smooth and occasionally blips. I also noticed that after driving for some time, oil has leaked out of the oil cap and can be seen around the top of the block.

This leads me to guess that my 940 is running rich or perhaps a misfire, as I have both good spark and fuel supply.

Any help is appreciated!