flat acceleration

Hi, recently the car would suddenly not go above approx 10 MPH, i have an 05 plate discovery. i have changed the MAF recently which sorted out the first issue, now vehicle has poor acceleration unless kept above 2000 revs, then it takes off like a scalded cat with black smoke out of the back end
any ideas what is going on.

Sounds like it's getting choked, so check air filter and all air tubing from filter to intercooler to turbo ...

You need to check for breaks, splits, and general gumming up. Dunno if the D3 suffers from the collapsing tubes, but if it does you also need to check the tubes internally for de-laminations. On earlier Discos this made a flap inside the tube which sometimes closed off air supply, hence over-fuelling, poor take off and clouds of smoke until it picked up and took off ...

Also, as a matter of course, worth checking the fuel system, filters etc ..

EGR valve.