Unclip the electrical connector from the injector and repeat your idle test. The fact that the sparkplug is clean points to an injector problem. Is it cleaner than the neighboring spark plugs? Might want to take the #1 coil out, put a sparkplug in it, and have someone crank the engine while you check for spark. If there's spark, then move on to the injectors.

You could rig up a "noid" light using a 12V LED. You can buy a universal one from Snap-On or Craftsman, but a 12V LED and a resistor are only a few bucks from Radio Shack. Up to you. Just make sure that the resistance across the LED is same or higher than the resistance across the injector itself or you will fry the drivers on the ECU. Add a resistor in series to get the correct resistance. Unclip the injector connector and connect the LED across the connector terminals. Then start the engine and see if the LED flashes. If it does, then you know for sure the problem isn't in the wiring. I would say it's a bad injector at that point. Good luck

Alin