I have not followed your saga, but was wondering if you might have a faulty injector. On injector could be out completely or maybe just putting out a bad spray pattern. If this were the case, your temperature sensor trick to lengthen the injector duty cycle might allow the other injectors to compensate.

Couple of tests:
Using a noid light or by listening with a rod or stethescope, confirm that all four injectors are firing.

With engine cold, start it up and monitor the temperature of the four exhaust runners. If one runner is not warming up at the same rate as the others, that cylinder is not firing properly.

Good luck,

Dan