Same problems as others connecting my Iphone6 to a 2013 Mercedes E350 and a 2013 Volkswagen Passat. Apple needs to fix this immediately!

What problem might that be?

My iPhone 6 connects perfectly to a newer car (2014) and an older one (2005).

I've communicated with someone having issues connecting an iPhone 6 to a MB and they found they had to remove the phone from the car list and then re-pair the device. Most of this problem comes from updating a device with the backup of an older phone. The phone retains the same name from the old phone, but there is a different hardware address when the device tries to connect to the car. Generally removing the vehicle from the Bluetooth list on the phone and then removing the phone from the list in the car and then putting both back into discovery mode corrects it. An additional step of resetting network settings on the phone may be necessary as well.

As usual, @ChisJ4203 offers excellent advice. I likely avoided the problem by having a different name for my former iPhone and the current iPhone 6, and also by having deleted the former iPhones from the cars before pairing the iPhone 6.

I had problems pairing my iPhone6 with the bluetooth on my 2012 VW Passat, as well. The phone was able to identify the car's bluetooth just fine, but when I entered in my phone's 4-digit passcode I kept getting a message telling me the code was wrong. Turns out it WAS the wrong code; the phone was looking for the default VW bluetooth code, which is 0000, not my iPhone passcode. Once I entered the correct bluetooth code everything paired up beautifully and has worked perfectly ever since.

Yes - same experience. In my Passat I solved the issue by just going to the radio panel, selecting the Phone screen and restoring factory settings which deleted the previous phone profiles. The iPhone6 then paired up correctly.