I've got an early mk8 that had a previous history of too frequent dpf regens. This could be a more commonplace thing. The dpf was deleted in the end and then there was a 'sooty idle' from the exhaust that got worse and worse. Hold the throttle at just above idle and the soot completely dissapeared. Then the idle smoke got so bad you had to every time pull up the last few yards each stop with the parking brake instead, keeping right foot on throttle revs just over idle and all is fine. Let sooty idle too long chokes up and a pig to restart hot. I got this van because previous owners had replaced everything but didn't fix smoke. Every time the identical problem. I mean everything, everything replaced even the entire engine and wiring loom, then finally gave up when an entire ECU set was tried but it didn't even crank engine. Every avenue of faultfinding had been tried nothing else to replace.
This gets interesting because since everything feasable has been replaced more than once it gives a blank canvas for experiment (where I came in). What I think as a theory may be going on is there could be a tendency (because of tight advanced emissions control) for this model to suffer from intake reversion at idle under some circumstances (to find out). If so that causes extra soot generation that trigger extra regens.
During every other TDC there's the scavenging period when both intake and exhaust are open, what's supposed to happen in that moment is some intake air sweeps out the exhaust before the intake valve closes. My theory is at idle there's a bounceback somehow that's blowing back during scavenging way beyond EGR amount. The combustion gets starved of burnable oxygen and causes the sooting up of DPF.
With the intercooler hose off at idle I can see puffs coming back out the intake. At idle the turbo isn't blowing them back in. I've got a suspisicon there's something going on with the exhaust somehow in previous history. Resonance or something that's not properly damped.