Ha, not only 8.1 DIDN'T fix the Bluetooth car issues - It created them!
I had a iPhone 5, which on 8.0.2 didn't pair correctly with my Hyundai. It paired, could play the music, but showed no network on the phone - hence - no calls possible.
Then two weeks ago i got a new iPhone 6 and restored the older iPhone 5, still with the 8.0.2 over the new 6. No reset of anything in the software - just restore of a backup.
Then - voila - the new iPhone 6 did pair absolutely fine - music, calls, calling list - the whole thing.
Then - yesterday, 8.1 comes, I foolishly upgrade and - bam! - no calling again - the phone pairs, it does show network, can dial, answer etc., but there is no sound going either way when I take the call.
So instead of fixing the issues, Apple just changed them.