OK, here's the latest update from the dealership:

After nearly two weeks in the shop, the service adviser says that they can find no problem with my E320. No codes, O2 sensors installed and operating, etc. I'm picking it up today. I have been instructed to run two full tanks of gas through the car, carefully recording the actual number of gallons used and the mileage driven.

You know, I have earned three technical degrees, (a BS and two MS's), from top US universities and I find the insinuation that I can't calculate fuel mileage vaguely insulting. I brought this car back to the dealership because of a fuel mileage problem that coincided with an emmisions system repair. I expect them to do more that just check for codes.

I will perform the experiment that the dealer designed to the letter keep the forum updated with the test results.

A question for the forum: If there really is twice as much fuel being injected as is stoichiometrically required, what other damage is the engine likely to incur?

FYI,

Steve