Had a rear wheel drive 2.4 duratorq doing this and it turned out to be a boost pressure sensor, it's a while back and if I remember it's mounted near the radiator,another thing maybe worth looking at is the waste gate on the turbo sticking/seized or play in the turbo itself,just a couple of things to check but firstly would probably give it a scan to see if any faults are stored,good luck
cdc, February 2017
