I had same issue with my new Car stereo Kenwood KDC-X993.
It would connect no problem and then disconnect randomly within the next 5mins.

I have solved this probem. I believe by disabling Power save option somewhere on my phone.

I am now able to get in and out. receive calls No problem with no disconnects. My thoughts is its the phone power saving fucntion shutting down systems one by one saving power even Bluetooth.
My screen saver power down is still active.

It will not however obtain Contact list and hass issues with USB connect and detecting my MP3s.

I hope this helps. just throwing in my 2 cents. And I appoligize for punctuation as my Original g15 keyboard. all my right Pinky keys do not work ie comma colon. I have tried to fix this to no avail.