Sorry for the delay. Good news, though. My mechanic (Mr. MB Motors in Tarzana, CA) checked out my car by hooking up a handheld monitor to the car's CPU. After a few minutes he declared the car was running rich and proceeded to use what looked like a very long screw driver (or allen wrench) and inserted it into a hole in the center of the air filter box. A few adjustments, a little more monitoring and he said "that should do it".
On my last fill-up, I recorded 310 miles (mixed and highway) on about 15.3 gallons. Much better than what I was getting!
Thanks for the tip on the vacuum hose. Even though my mileage is better, I'll have him check it out next time just in case.
2001 Porsche Boxster
1991 Mercedes 300e
1971 BMW 2002
2000 Mercedes ML320 (wife's!)