Why is my Ford Ecosport petrol engine sputtering sporadically?

I have a 2013 Ford Ecosport 1.0L petrol engine. It is turbocharged. Recently, around the time of my 120000 km service, I noticed that the car would sporadically sputter. The sputtering happens at different speeds, different gears, and at differing acceleration. The problem comes and goes from day to day (some days I do not experience it). I mentioned it at the 120000 km service (done by a Ford service centre), but they did not pick anything up in their diagnostic test. I though maybe the service would sort it out but the problem persists, but is unpredictable and cannot necessarily be reliably demonstrated to a mechanic. Any ideas what I could ask them to check?
Thanks.