My '06 650 BMW has 71000 miles and smokes when allowed to idle for more than a few minutes. It does not smoke when accelerated from a slow speed. What's the problem?

Like tom said where from? I will assume the tail pipe if thats the case you have two options. One you need to check your crankcase valves for being torn. If those are torn it will cause excessive crankcase vacuum and actually suck oil out of the oil pan and burn it. Second is more expensive issue. The valve stem seals have hardened and are leaking oil down the valve and burning the oil. This is becoming a more frequent issue with the N62 engine.

2007 BMW 650 smoking out of one pip what it is