After replacing the throttle body with no effect (thanks BMW for your great onboard diagnostics) I checked every fuse block and connector for signs of water, mice or other damage. Couldn't find anything. Discovered there was no power to the coil so began checking ECU wiring. Found the Main Relay wasn't getting its triggering ground signal from the ECU. Bypassed the relay and the motor started right up! Discovered the small brown/red wire going from the ECU to the relay socket had no continuity. Began peeling off the cloth harness wrap and about 3 inches from the ECU plug noticed a small pinched section of the wire. Clipped the wire and stripped it back to find about 1/4" of corroded wire. Cut out the bad section, soldered and heat shrunk a new piece of wire in place and I now have continuity! Took 17 years and 210,000 miles for this small wire to fail but I'm glad I found it without further pain. Now I have to put everything I took apart back together!

Lesson of this story is to pretty much ignore what the Diagnostics tell you and don't go throwing parts at the problem ($240 for the throttle body) but carefully check out the wiring system.

Eric