I'm by no means an expert but at least it's promising that you did get it to connect although briefly.
I would in order
1. delete the connection on both the iphone and the car you are connecting to
2. hard reset the iphone (home and power buttons simultaneously) - may not make any difference but........
3. rename the iphone in itunes (important step)
4. pair the iphone with the car
5. turn on show notifications (hopefully it shows up)
6. cross my fingers as I'm then out of options
I know it's cold comfort but it works on my iphone 4 so there is hope and bluetooth is meant to be a standard but I'm sure each device can have its slight differences
Good luck
Peter