I got around to checking the water temperature sensor today with an analog meter so my results are not very accurate, but I'm pretty confident that the sensor is a goner based on my results. The sensor on my car is the (thankfully cheaper) 4-pin CIS type.

I checked the resistance on opposing pins on the temp sensor. With the engine "cold" and ambient temperature around 26 degrees centigrade, I got a reading of 4KOhms. With the water temperature gauge on the dash reading roughly 80 degrees centigrade, I got a reading of roughly 1.7KOhms.

If I've read past posts correctly, the fuel management system is basically being misled and is assuming that the car is running at roughly 30 degrees centigrade when it is actually around 80. I don't know at what temperature the system decides to stop running rich, but 30 is pretty cold for an engine so I think that might be my problem. Could someone please confirm that the water temp sensor used on my car should give readings as follows (copy/pasted from one of Marty's old posts):

Degrees KOhm
20...........................2.5
30...........................1.7
40...........................1.18
50...........................0.84
60...........................0.60
70...........................0.435
80...........................0.325
90...........................0.247