car bluetooth problems with iOS 9 update

Since doing iOS 9 update my iPhone 5 won't reliably work in my car (mercedes benz clk with bluetooth adaptor)

previously under iOS 8 it worked perfectly pairing automatically when in car, and diverting calls to car system both incoming and outgoing all worked flawlessly even

siri would work through dashboard microphone

now it is total chaos

some times it works immediately, some times it refuses to work at all

most times it is unpredictable and often requires toggling blue tooth on and off on both phone and dashboard until ringtones heard through dashboard speaker system

what works in the morning won't reliably work in the afternoon

if tried reset phone

forget this device

repairing

not sure what else i can try

wish i could down grade back to iOS 8

rob