ive got a 2.0 golf gti and ever since i brought it its lumpy on idle and on acceleration isnt always a quick take up the revs i was wondering if it could be a blocked injector also a few weeks ago i was on the motorway and poot my foot down and at top end there was black smoke on acceleration then i let off and accelerated again and it happend again so i pulled over reved it up for a min then no more smoke any ideas guys?