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You've mentioned the A/C a couple of times but it isn't clear whether you've done this test:

With the engine running but while it's still cold, if you switch on the A/C then that will cause the cooling fans to come on at low speed. If you allow it to run for a couple of minutes to let things settle down and then switch the A/C off, does the engine still nearly stall?

That would seem to be an easy way to eliminate the ECT sensor and the associated portion of the PCM circuit which triggers the fans to switch on and off.

If it still stalls then that would suggest that the ECT sensor circuit is not the cause, but if it did not stall then that would suggest that the ECT circuit requires further investigation, and it would also tell you that you don't have a problem with spikes at fan switch-off.