think its a head gasket.

It seems to be the breather (PCV) valve failed. This is not an easy, simple process to change it. I strongly suggest to find a good BMW specialty shop to check/repair your car ASAP. If you keep driving with a failed breather valve you might need to replace the O2 sensors and the catalytic converters also, which are expensive items. After the intake hose removed and the throttle plate is open you should be able to take a look inside with a good flash light. If the valve is bad you will see lots of oil inside of the intake. Zee

I've had a cimalar problem and found that one of the Lambda cencors on the exhaust to be faulty. After changing it, smoke stopped and the idling became normal again. No more roughness. It also changed the mpg per tank!