My wrx has recently started black smoking. When i put my foot down there is a big initial puff which seems to clear as the revs build. The car is also giving increased knock reading when i lift off and when on part throttle the knock reading seems to jump around, most noticably when motorway cruising. I had the engine rebuilt by a well known Subaru specialist a little over a year ago and changed all the coil packs the same time, as the car has individual ones. It also had new injectors and a Lambda sensor fitted the same time. The car has also had a new turbo a few months back and has been remapped by the best in the business, a certain scottish gentleman. Everything has been going great until now. The car is also making a slightly different noise when starting, kind of like the starter is breifly slipping and i'm sure i'm detecting a slight missfire at low revs. My thoughts are going along the lines of spark plugs, leaking injector seal, MAF problem.
Any ideas you guys have as to whats causing the problem will be greatly appreciated, especially if someones had this problem before and rectified it. Thanks for reading

 

BTTT for the sunday guys.