Good questions, I didn't noticed it myself in first instance.
I checked the swirl valves on the top of the intake manifold. First thing I noticed was the bar which moves the valves was laying on the intake manifold (not onto the valves). Next thing you see is a black messy some sort of 'paste' around the valves. I know intake manifolds, normally they are just 'clean'. When I saw the black wet mess on the manifold, I have checked the valves with a screwdriver. Very easy to test. All were moving (one very hard), but my luck was that the bar had come off (so no rare engine faults). All the valves had a lot of play, which isn't good, simple: just faulty.
The manifold INSIDE was full of gum too. Throttle body very dirty, and the inlet on the manifold as reduced to what I think was a big 2 EURO coin (yes... We don't have pounds... :-) ). The inlet of the EGR was also almost stuck. The black mess inside is so hard to remove, I don't believe you can ever clean it with something you just spray into the manifold. And when it DOES, all the black mess will go into your cylinders and through the turbo... Bad thing...I kept cleaning the throttle-valve for 5 minutes with brake cleaner and a toothbrush...
The engines (I think) won't last for 400k kilometers with the EGR on it. After 200k (now) it was so full of the gum, I'm worrying about the turbo.