Steve --

Tony's got a head-scratcher. I agree with you, that cleaning and checking those connections would be good practice -- particularly since he just installed a harness.

The dilemma is this: These sensors have a negative coefficient. That is, lower temperature means higher resistance. And when the resistance is high (meaning cold) the ecu enriches the mixture -- sometimes to the point of totally flooding the engine. Corrosion or bad connections would increase the resistance simulating very cold conditions. I've seen this on several cars.

Tony's problem sounds, at least to me, like the opposite -- too lean upon start up -- he says it "stalls and backfires". Wouldn't this mean the ecu is forced to think the engine is hot? As you said, perhaps he's faced with simply a defective sensor, or maybe the wires (or connectors) are touching instead. This would lower the resistance, and the ecu would think the engine is hot and lean out the mixture.