Originally Posted by BimmerM3inGA

A quart of oil per week? Well, as they say, "There's yer problem!" That is not normal oil consumption. The M54 engine in your X5 is known for being an oil burner, but not to that extent. You may very well have fouled plugs causing your misfires.

The oil separator, also known as the CCV (crankcase vent valve) is a system of plastic/rubber tubes and the actual oil separator itself. It circulates crankcase vapors through the intake manifold to burn them off. Some engine oil also makes it into the system and is separated from the vapors and drained back into the oil pan. These rarely last much past 100K miles and are a very common cause of vacuum leaks. In extreme cases, it's possible to actually suck oil out of the oil pan and feed it into the intake manifold.

These systems and their problems are well documented. A few searches for "BMW M54 CCV" will provide lots of very informative reading material.