Yeah.it's a problem with the S4. It will automatically connect to car audio as phone only and not media. I have to manually select media under bluetooth setting. My nexus4 connected both without issue...
Having the exact same problem with an aftermarket Sony Bluetooth Deck. So annoying! What did you reset, your phone or your car audio? Did you do a HARD reset where you wiped out all the information on your phone or a reboot? Thanks!