Can anyone help identify this problem with my E93 330i in case I can't replicate it at the dealership? At idle after a cold start the revs will fluctuate between about 800rpm and 200rpm (without any throttle input from me), when it gets down towards 200rpm it nearly stalls and then jumps back to above 600rpm and then drops back into its stumbling idle again. This has only been happening this week and I've got it booked in with the service for Monday. If I blip the throttle up to 2,000+ rpm then it settles back down to its proper idle, 700-800rpm. A friend thinks this could be related to the swirl flaps getting stuck/failing but I've no clue.
Another oddity that seems to be related is that one time this also came with a squeaky/whining noise (not as high pitched as a fan belt squeak). I'm not able to replicate this but it has also occasionally made this noise under light acceleration, the whine lingers for a few seconds after lifting off the throttle then is gone.