I guess I just don't see the point of all this trouble...when I bought my '98 it had 115K miles on it and I had the intake cleaned out. I watched as the tech scraped out a layer of black crud with a knife. It wasn't all that thick, maybe one or two mm and it was not hard to remove. According to the records I had that would have been the first time it was done.
Last December, at about 140K miles or 25K miles later I had to remove the intake to replace some fuel lines and IP DV seals and the intake was still pretty clean with just a film of black oily layer on it so I didn't even touch it.
So it looks like it only needs attention about every 100K miles...is it worth messing with the engine and possibly doing other damage to avoid having to clean an intake manifold every 100K miles? Even if you wanted to be super diligent and do it every 50K it would not be all that hard to do it. I can now remove the IM in about 15 minutes and replace it in about the same time so cleaning it out really isn't too bad a job.
It's also possible that with the new ULSD there will be even less crud built up in there too...I'd say leave it stock and avoid dealing with possible troubles...that's my $0.02 worth of advice.
BTW - I just returned from a 2200 mile round trip to western NC in the E300...it performed flawlessly...never gave less than 30 MPG even at altitudes of up to 5000 feet with A/C blasting and I don't anticipate removing the IM again until 200K miles unless something goes wrong before then.
The car has been amazingly well behaved in 2007...I've literally done nothing to it other than replace the oil/oil filter and spin on fuel filter in the last 12K miles. And the fuel filter was purely as PM since I used some B20 and wanted to prevent any problems on my trip. It's finally running like a
real Mercedes
