Hi - my A6 has the 2.5 TDI 150BHP engine. It's done a lot of miles now (170K) and has started to smoke a little. It doesn't do it at start up but it's noticeable in evening traffic at sub 2k revs. Smoke is dark in colour. No loss of power - other than an occasional slight judder at around 1500 revs. It revs freely and doesn't smoke at speed -other than the to be expected smoke when flooring it. As an example - going through a 50MPH speed limit in 6th it will start to smoke heavily - drop down to 5th / 4th but maintain speed and the smoke goes. No codes showing in vagcom. Any ideas where to look -wondered if it's turbo oil seals..but the turbo has no boost problem and the smoke is not blue ? I wondered if it's a stuck wastegate but not sure if this car has a wastegate ? or if it's EGR valve sticking open ?, or it's N75 - but from what I read that seems to come with a drop in power so think I can discount that one. Best guess I have at the minute is dodgy injector - but would this explain the smoke stopping at circa 2k rpm and higher and the occasional judder at 1500 rpm ? I'm tempted to stick a bottle of injector cleaner in it to see if that helps ? Appreciate any thoughts ?