Just drove the 99 E300 with the low MPGs from SF to Colorado - still in the range of 23-29 mpg on the highway, but also noticed some really interesting behavior that cemented my opinion that there are issues with injectors and/or the fuel controller:

At high altitude, the car started making really strong clattering noises for several seconds each time I released the accelerator at low RPMs.

And, crossing Vail Pass (10,000'), the car was smoking (white smoke out the exhaust) like crazy between 2000-3000 rpm (and also surging a bit); dropping it into 4th gear and keeping the revs up got rid of the smoke.

So, the injectors are clearly dumping too much fuel. Two questions:

1) Does the 99 E300 have any altitude compensation (and/or is this "normal" behavior)?

2) The car is under warranty, so I'm going to take it in to have work done - anything I should specifically look/ask for? (I stopped at the dealer in Denver and they said that they suspected a "dripping injector" but that they had to open up the engine and look, and it would take 3-4 days for them to take care of this including ordering parts).

Thanks...