BMW Repair: idle vibrations of M62 TU motor in 540iA, mass air sensor, crankcase ventilation

Question
Dear Evan,
I have a question regarding a problem which is in my BMW. it is a BMW E39 540iA Built in 2001, VIN 7 digits: GG91066. It is the european model, as you will see. Where i live, in Hungary, i went to several service of BMW and they put my car on the MoDic and showed no faulty code or anything. If the car is warm, the idle rpm goes down to 500 rpms, and you can hear slight vibrations and feel them when you touch the motor, and you can hear them by the exhaust, like if the engine would misfire. It is not the ignition coils, not the mass air sensor, i have new spark plugs, new catalysator. if i put the A/C on the level of rpm rises, but the vibrations still exist. If the A/C is off, the rpm goes down again to 500 and you can hear that the engine wants to stall, and if in P-park, I press the gas pedal a bit, for lets say 1000 rpms, and let it go, the needle will move to 300-400 rpm, and then to 750, and then back to 500. and sometimes it even stalls. Now maybe that is in conjunction with the vibrations of the motor or maybe not. What can this be the cause of? The experts in BMW services only put my car on the MoDic, there is no fault, and the service guys say that the car has no problem. I really do not know what could be the cause. Maybe the crank position sensor, where i have two of them on the sides of the motor block, and i actually disconnected one, and the car showed no fault and ran the same way as if it would be plugged in, only if i disconnected both of them, it wouldnt start. Also if when the engine is idle, and i take off the oil cap, the engine runs very ruff, but the same vibrations occur only in a greater amount. Now, maybe the engine is receiving wrong air from the intake hose or whatever. If you would like i can make a video with the problem, if you know what my problem is.

Many thanks.
Laszlo.

Answer
Laszlo, I would check for intake manifold leaks and the crankcase ventilation system. The crankcase ventilation valve is integrated into the rear cover of the intake manifold. I would use a smoke machine or can of brake cleaner/carb cleaner and spray around the intake gaskets throttle gaskets and such. If the idle changes momentarily then you have a definite leak. If you have oil/dirt build up around the seams of the intake I would encourage you to do this anyway. Get all the gaskets for a complete intake manifold reseal (intake runner gaskets x4, Front plate gasket, Rear backing plate and gasket, throttle body gasket.) I would also clean the throttle body with some brake cleaner or acetone. A dirty throttle can affect idle, but not to the degree that you speak of. Get yourself an oil and filter change if not done recently. I am surprised that you have not had a check engine light yet. Those sensors that you unplugged were the Camshaft position sensors. They are regularly faulty, but always throw an engine light and the car misfires severely. The crankshaft position sensor on you vehicle is on the transmission bellhousing and if that is bad your car will never start. Let me know how it goes.
P.S. your grammar and English are very good.
-Evan