So you are saying that all else did fail...
I am no expert but found this:
Driveability symptoms that result include poor startup, engine stall after startup, poor idle, engine stall at idle, poor throttle response at throttle "tip-in" or possibly even engine "ping." Besides those things, you may also discover that you are unable to access the vehicle on-board diagnostic tests, and/or unable to properly set the ignition timing!
My mechanics says the same, and I don't like it, but guess there is a good reason for it..