you could try d/l the app 'Bluetooth File Transfer' and try to pair the car using that app instead of stock app.
I have same phone and same rooted 4.2.1 , there definitely seems to be a problem. Sometimes my phone connects , sometimes it doesn't. If it doesn't and I turn my BT off on the phone , it hangs and have to reboot to connect.
I do have BT speakers in my house and it prefers to connect to that first so maybe there is some mileage in deleting all BT devices from the phone apart from the car and see how it fares.