2008 Peugeot 308 jerky, hesitation when engine cold

I have had a 2 year old Peugeot 308 for 1 year and it has had a problem with running rough from cold, for the first minute or so the car jerks and hesitates down the road. The garage had it in last year for a full week trying to find the fault, they told me that a software download had been done, an adjustment to the timing carried out and that the computer now said that everything was fine. However it was not much better, I put up with it until the car needed its first service last week when I told them about the fault again. This time I told them to drive it from cold instead of plugging it into the computer and they might discover the problem for themselves. They did indeed experience the fault and downloaded another software upgrade but the problem was still there. They then, after phoning me, put in a new set of plugs in which mostly cured the problem There is still a slight hesitation problem which the garage tells me is "normal for an engine of this type". Is this correct?.