Valve stem seals cause smoke on start up because oil sitting on the top of the valve stem will drip down past the intake valve into the cyl head chamber where it burns on start up. This happens with the engine off. You see the accumulation of oil burning on initial start up then it calms down once this has burned off.

At idle you have the highest vacuum signal in the engine. This is when oil is pulled into the intake manifold if you have air leaks in the engine.
You rev the engine and this oil in the manifold goes into your cylinders and burns making blue smoke. Oil does not belong in your intake manifold. If you just take 5 minutes and remove the hose from the front of your intake manifold and look inside you can see if there is oil in there or not. Look in the hose also.
If oil drips out and you see wet oil in the manifold you found your problem.

Third scenario, you are going down a hill in your car with the foot off the gas, you hit the gas after this and blue smoke comes out. This is normally piston rings failing.

A fourth thing to think about. If you pull your spark plugs out and 1 or 3 have heavy black carbon on them and the others are clean this would be an indication of valve stem seal failure. The bad plugs are running in cylinders with high oil consumption.

This spark plug test is a good indicator of how well your engine is running.
If all 8 look equally good your oil issue is spread out through all your cylinders again pointing to the PCV or Positive Crankcase ventilation. Again, BMW calls this something else but crankcase ventilation is what it does. If oil is beng sucked into this system it hits the manifold where it will go all through your engine to be burned not just into one or two cylinders so all 8 plugs will look pretty much the same.
Before we fixed my son's car he came home from college and told me his valve stem seals were bad. He researched it on the BMW forums.
When I asked how he knew it was valve stem seals he said everybody on the forum told him it was a common problem. His 4.4L was at 140,000 + at that time.
I told him to pull the spark plugs and look at them. They looked brand new but he was burning a quart of oil in less than 500 miles.
I told him it was not valve stem seals and being smart and in college and with all the notes on the forum backing him up we discussed this issue for a couple days. ( argued ). I showed him the wet crankcase vent and oil in the manifold. I finally convinced him to just seal it back up, he had several oil leaks. He fixed it in stages as he had parts and time. One valve cover, then another, then O'rings etc over a couple months. Oil consumption kept getting better and his engine kept running better and shifting better. His was getting 24 MPG on the highway at 75 MPH pretty consistently on his trips back and forth to college, once the final oil leaks were repaired he no longer burned oil.
His intake manifold was very wet with oil inside on tear down and was not easy to clean. Hot Soapy water and small scrub brushes and a lot of time got his clean again. If we did this again I would pour solvent or diesel fuel inside first and swish it around for a while, dump that and then start with hot soapy water. If it is wet with oil it will attract dirt, you want it clean.