VRS

I have replaced aux belt and tensioner, since doing so i now have a fault which causes difficult starting when cold and cutting out.
I believe the job was done properly and as the crank sensor is no where near the tensioner. The fault was not there before but i accept it could be a coincidence.
I have ran an ids self test which initially came back clear. Then yesterday indicated and frp fault. Have taken to a diesel diagnostics specialist who have said there is a pats fault.
9681/0191 tranceiver not connected.
Bought car back re ran the ids test as a global and only fault present is brake light switch.
When car does start it runs rough and will cut out if revs fall below 2000 rpm.
Any advice will be greatly appreciated.
Regards
alex