First off that "hot" CHT value is not good (I assume by "hot" you mean running for at least a couple of minutes or more). I'm surprised the car would even idle with a resistance that high. It would be running pig rich. If you reduce air with idle bypass screw with a rich condition you end up with an even richer condition and probably stalling.
Also, just to be clear, the ECU doesn't "sense" a rich or lean condition. It's not a closed-loop system like modern FI. It's simply designed to provide more fuel (through longer injector pulses) when the engine is cold/cool based CHT resistance.
This is from someone else's thread, and even though your CHT (xxx-03, IIRC) isn't on the chart, it should behave similarly.
Could be a bad CHT or a break in the wiring harness. You should trace the connection from the sensor all the way to the ECU to make sure there are no breaks. If none, I'd remove it, test it out of the car, and replace it as needed.
You didn't mention which way you turned the ECU knob (CW or CCW). It has a relatively minor effect that's not going to overcome a bad CHT, but out of curiosity which way did you turn it?