Hi. I've been having the same problem for last couple of months, went through everything, got injectors leak off tested, checked engine mounts, checked power steering fluid, checked drive shafts all ok, changed MAF(mechanics £250 hunch
), I give her full pampering(engine flush, new oil and all filters replaced, removed cleaned and blanked the EGR, added Redex to fuel) all had no affect what so ever,
My mechanic -"Alfa Romeo Specialist" tried to convince me the vibration was in my head...
I plugged her in to MultiECUscan after buying interface online, injector correction values were off the scale at idle +2 but went back to almost zero at 2000rpm.
I took her back to mechanic to redo the leak off test again he found nothing wrong.
I decided to take it on myself and removed the injectors and took them to independent diesel tester who bench tested them, all four were out of spec. He said it may not have been picked up by leak off as all injectors were returning similar amount of fuel all be it too much...
Long story short, Plug in to Multiecuscan and check correction values, this will highlight if injectors are at fault, if in doubt remove and get bench tested. Don't be shocked if all four are done as my car was driving fine with plenty power with the exception of vibration on idle which started suddenly and it was a bit smoky on start up.