Oil smoke is blue, Coolant smoke is white and smells sweet and a rich condition smoke is black and will burn your eyes.

Vacuum leaks don't come and go. Engine should go from open loop to closed in about a minute or less. A closed loop indicator is when the engine drops to a normal idle after a cold start. At an idle the loss of proper vacuum will be most prominent. Smoke test is the best practice to find a vacuum leak if it isn't obvious. There are several examples of how to make an inexpensive smoke tester on youTube. I made one from the video using a paint can and a propane pressure adjuster, has never failed me. I think it was made by the fifties guy.

If you aren't using a zero-20 weight oil in very cold weather that will cause the oil pressure to be low after a cold start but it shouldn't take that long to become normal. Must be sure the oil is not low. Don't assume it is low, verify one way or the other. Normally, if the oil is very low the engine will clatter especially after a cold start in cold weather. A valve cover leak would have to be huge one to lose a lot of oil in week or two.

Even though you addressed the CCV a few years ago it still could be a problem especially if you seldom drive more than 25 miles before it is shut off and not started again for several hours. The oil won't get hot enough to evaporate the condensation. Check the oil to see if there is an indication of coolant and the coolant for traces of oil. If it is very hard to remove the oil fill cap when engine is running that is a symptom of bad CCV.

I don't think the stalling has anything to do with oil pressure. Sounds to me like a air/fuel ratio issue. That would lead me to an MAF problem, O2 sensor or idle control valve, or certainly a vacuum leak. I don't think if is low fuel pressure or you would have the starting issue with cold start or otherwise.

Have you checked for error codes? The shop said it was not a serious problem when it could stall and not start when you are out in the boonies or on a busy freeway?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas