Well our own TA (build date 20 September 2012, registered July 2013), the oil for that is definitely 5w40 acea c3. We had no issues whatsoever with rough running after its first service in August last year, indeed from what I remember, it seemed to be a little smoother and sweeter sounding after the oil change, so not sure why yours should be any different after a oil and filter change. Do you know the build date of your own car? Just ask your Fiat dealer to let you know its assignment date if you don't.
I'm assuming here you have used a Fiat franchise dealership for the service?
Thanks, yes, an approved indie that I have a good relationship with. The oil has always been contentious as the car was built in week 51 of 2013, the fiat system says use 5w when you enter the vin and I had my indie confirm this with fiat but who really knows what the car was delivered with. I also noticed today that they were quite generous with the oil and its a bit over the max mark which may not be ideal, anyways I'll see how it behaves on a cold start in the morning.