My limited knowledge on the subject is that the swirl flaps are on the fresh air inlet and controlled by a plastic rod that is prone to breaking on some Mercedes.
The M272 petrol V6 has a very similar issue - there's a plastic linkage that operates a ramp inside the inlet manifold, varying the distance the air travels depending on engine rpm. The mechanism clogs up with carbon over time (making it harder to move) and eventually the linkage snaps, putting the EML on. You can buy aftermarket repair kits consisting of a replacement metal linkage, but really you need to remove all the carbon from inside the manifold. The MB fix is simply to replace the manifold (we were quoted around £1000 for this after a 40% labour discount).
Glad you got yours sorted in the end - with that sort of mileage I'd also be suspecting a sensor problem, but a new manifold FOC is clearly a decent resolution! Hope this one lasts longer ...