My 760 turbo wagon began to suddenly cut out a few times while running errands for a few hours, and would then return to normal. Several days later, that symptom stopped, but the idle would go up and down. Last week, suddenly the idiot lights came on, the engine quit, and refuses to start. It smells like gas.
The shop I had it towed to said that fuel injection system supplies too much gas for no reason, and that the ignition and fuel supply systems are test ok. They placed their bets on the air mass meter ($350 to replace; it apparently can't be tested) or a short in the main engine wiring harness ($800 incl labor). I received a message today that the air mass meter replacement didn't fix it, and the car still won't start. I am reluctant to replace the harness due to cost and lack of assurance that will fix it. I've read similar posts, but successful repairs seem elusive or the owners haven't bothered to share. Anyone has any ideas other than these? Thanks!!

Possible causes suggested elsewhere:
waste gate linkage
air mass meter
fuel pressure regulator
failing iac idle air motor
dirty intake system/throttle body
ECT temp sensor
clogged/leaking injector
oxygen sensor
temp sensor