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Are you sure that both of your fuel pumps are OK? I had a failing outer pump, and it would run bad intermittently.
Just brainstorming the situation- if it is running lean due to fuel starvation, the engine may race- but setting it back to default by pulling the ECT may allow it to run normal because of the rich mixture.
Try pulling the connector on your in-tank pump in the trunk, and see if it still runs (you should have enough of a reserve in the outer reservoir for the outer pump to run if it does run.
If you already have a new ECT sensor, have you tried replacing the front O2? That should be the only other thing that would throw the system off really rich, that could be corrected by putting it back into open loop. If it were a mechanical issue causing a rich condition (free flowing injectors, burning oil, etc) I wouldn't think you would be able to reset it.
It's hard to test an O2 sensor, since the voltage it produces is pretty low. It should fluctuate, up to about half a volt normally.