Drinking too much
beer in Munich ;)
Join Date: Feb 2012
Location: I would rather not say
Either the EGR and/or swirl valves and swirl valve actuator lever.
The swirl valves (tumble valves) should be closed at lower revs and open up as the revs rise. If they cannot close properly at lower revs the engine produces less power at the bottom end of the rev range.
They get gunged up by the recirculation gasses passing through the EGR valve, so not only is the EGR a likely cause of the problem it is possible that it makes another problem elsewhere in the inlet system.
Swirl valves can be cleaned in situ with carb cleaner, but really badly gummed up ones need the inlet to be removed.
You could also have a choked up DPF. Performing a forced regeneration cycle on it's own ought to produce a noticeable difference if that is the case.