When I received these codes they both were related to the intake system. You might be lucky and have a vacuum leak, mine were related to the crud built up in the intake manifold. The EGR wasnt opening and closing properly, along with one of the switchover valves. I would start by taking off the EGR valve, clean the flap good with brake cleaner and see if that resolved the p0400. You really need to get it diagnosed to see if the "Induction Pipe Switchover Valve Y22/6" is really the culprit. I would subscribe to www.alldatadiy.com and get a good look at the whole intake system before dissasembling. You can also do a search here.. Keep us posted

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Dennis
2006 E320 CDI Black/Black Leather. Nav, HTD Seats HK stereo 32000 miles.
2000 VW Passat 1.8t 300,000 miles as of Dec 09, 2009 original owner
1997 E300d Silver 300,000 miles As of Jan 05, 2010
3rd owner SOLD