Well sounds funny but I will tell you it had me stumped. My 2001 740i would stall on cold start ...usually twice then would run but a little rough. after a brief time it would make this strange vacuum leak sound that I can only explain as a UFO. I checked and checked but gave in and took it to the dealer...It ended up being the Oil Seperator under the intake...OUCH! $930.00. $575 for labor. Well it was in and out in less than a day and the folks at Autobahn BMW in Fort Worth Texas are what I would say OUTSTANDING.