We had that issue start around 16000 miles and brought in several times where multiple dealerships said they could not replicate. In the end they did acknowledge the problem and replaced our EGR valve and something else and supposedly that fixed it (sorry threw the documents away). It was in the shop regularly for about four months to actually get it resolved. We sold it this summer shortly after because it was obvious that here in the U.S. diesels seem to be like a spaceship from another planet. We loved the car otherwise but were down to less than 12k left on warranty I wasn't willing to foot the bill while BMW techs try to figure out the diesel and give me the runaround.