I have the same problem with my iDrive 2006 330. Bluetooth was working, then it stopped.
Drove to the dealer, the guy erases all the phones, wipes the car from my phone, pairs it again, everything works! Or so I thought... A few days later the problem shows up again, phone can't pair with the car.
Here's a couple strange things I've noticed:
First, it's not a phone issue. We had this problem with four different phones, a Blackberry 8300, another Blackberry, an 8520, an iPhone 4 and a Samsung Galaxy.
Second, it appears to be totally random. A couple times I was able to get the car to connect by doing the three finger reset, but as of lately this has stopped working.
Sometimes the car would connect, you start a phone call and halfway through it a strong noise (a buzz, if you will) comes through the speaker system and you lose the BT connection. The call continues on the phone, I was able to continue the call picking up the headset and hang up at the end, but strangely the car is still acting like the BT call is on - Radio off, call timer counting. The only solution is turning off the car.
Then I found something else: when the car and the phone are not pairing, if I go to the Bluetooth settings page (the one with the little checkmark to disable Bluetooth) and try to disable it, it won't respond.
So, that's my rule to know whether Bluetooth would or won't work on any given day: if I can uncheck BT, it will work. If it remains stuck, it won't. (I'll try to snap a pic and post it later, I don't even remember the exact name of the menus and options, hopefully you'll get it). For those of you on iDrive and a similar problem, see whether you can uncheck the checkmark.
Now for more randomness. I gave up on Bluetooth, but then I'm driving and once in a blue moon my phone rings through the car speakers! I answer and have a normal conversation. Sometimes it goes all the way, some other times it crashes halfway through. So it's still working, albeit randomly.
Now... don't laugh at me... here's what I've noticed: Bluetooth seems to work in the winter, but it quits working as temperature rises in the Texas summer. This year, for the second consecutive year, Bluetooth worked between November and March... In other words, what I'm saying is that if it's cold outside, my phone would connect. If it's hot, it won't.
I know it doesn't make sense (well, maybe it does, more on this later) but that's my practical observation...
I mentioned this to the dealer, who almost laughed me out of his office and said that I need to reset / re-pair everything. Obviously the idiot doesn't know squat about this problem.
Now, as for the Summer / Winter issue, sometimes a connector, a bracket or another car part may expand in the heat and contract in the cold. This issue has been known to cause connectivity problems in computers (card and motherboard), so why not my Bluetooth module?
The car is going back to the dealer in a couple weeks for an unrelated issue (program a new keyfob, wife lost hers) and we'll look at it again, I'll keep you posted if I get any answer.
In the meantime I've tried a couple things: the car was unplugged for a good time when the shop replaced the battery but BT didn't come back. I checked the connections to the computer (including the fiber optics) and other computers, but that didn't make a difference either. There may be other tests to perform or other ways to access a maintenance or error menu but I don't know what they are. Any suggestion is truly welcome.
Did any of you experience the same problem? Thanks for your help.