Why was the Passat 'Smoking'?

June 30, 2016 WHY WAS THE PASSAT 'SMOKING'? - Andy Horwat, EngineTuning & Diagnostics, Swindon (Reproduced from PMM Magazine, June 2016) VW Passat 2.0D - Black Smoke Emitted and Misfire on Idle I was recently presented with a VW Passat 2.0 D that had 225K miles on the clock and was fitted with a Bosch EDC 1.5 system. The main symptoms were hesitation and misfire on idle and I was informed that both the turbo and EGR valve had been replaced six months previous. Armed with those facts my first course of action was to check things over with the scan tool and look for any DTCs. I found none that were of any interest so I then took the car for a test drive. In this instance I decided to leave my scan tool connected, and I didn't have to drive too far to notice that the performance was very poor with a lot of black smoke emitted at the same time