The easiest thing to do would be to measure the reference voltage at the cts plug, as if low it will cause problems.
The next thing would be to use a 1 watt metal film resistor across the two terminals to "fool" the ecu into thinking a normal temp was being read, but you will need to look up the resistance versus temp of the sensor/engine.
I think it more likely that something else has changed, that affects the fuelling, so certainly don't discount anything, maybe something easy like a pipe come off somewhere.
Is the map correct or a base map ?, what loom are you using ?
tabetha