Need CLT troubleshooting advice

[gboezio]

I'm chasing a (very) intermittent problem, the cold engine light comes on while I drive and I got a 0125 code only (engine too cold for closed loop.)
So I tapped a twisted pair on the sensor connector and hooked it up to a multimeter, reading DC volts while I drive, I can clearly see the voltage going from 2,4V cold to about 0,450V at diving temp.
But when it does goes cold I would expect a High voltage, but in fact the voltage drops to about 0,300, this triggers a high idle (2500), (havent checked the rad fan) and the cold light while in fact I should see the hot light. This happens for seconds to a few minutes and the voltage have no transitions, it jumps instantly, no special condition cause this it happens randomly.
If I short the sensor to the ECU, the voltage goes to 0 of course and trigger the cold light, rad fan and of course the CEL, but no high idle.

My question is if it's normal for a high temp to trigger the cold light since a hot light exist on the dashboard, the voltage is taken inside the ECU from the 5V ref sent toward the sensor, I'm beginning to think that the 5V supply is dropping low, but this won't explain why the ECU trigger the cold light.

I'm lost and start to think that the ECU is going south.
Thanks a lot for reading this and thanks double to submit stuff I could have missed.