C220 very smokey
 

HELP! I have a 02 c220 cdi which is puffing out black smoke, a few months ago it wouldn't pull over 3k revs, left it with mechanic, new MAF fitted car is now revving ok but now is smoking really badly. at idle the engine revs will drop slightly then rise and then fall to arround the normal, when this happens it puffs out a cloud of smoke also when driving with only slight pressure on the accelerator pedal the car jumps and splutters but clears when the pedal is pressed down. can anyone help!!!