That's an interesting puzzle. If you want my $0.02 cents on it check the knock sensor or unplug it for a bit and see what that does, alternatively replace ignition coil for that cylinder, cable, cap and plug.

Those would by my main suspects if it works well in open loop mode, knock sensor first.

If it runs fine in open loop mode, it sounds likely to be a bad knock sensor causing the ecu to think there's detonation and retard the timing to the point it doesn't fire at all. As far as getting it into open loop mode, unplugging the throttle position sensor or any of the other intake sensors (MAP, Mass airflow, etc) would probably get you there.