I found the 4 prong one for CIS/EZL right under the air filter housing. Got about 850 ohm reading across which says I am in the ball park (840 ohm @ 50 C). I will do another reading tomorrow morning when the car is cold and I should get about 3K ohm.

I felt kind bad after all this trouble, all I will accomplished for $70 is changing to the right coolant and able to read the temp right. It has nothing to do with how the car is running. Man, I had hope I could get rid of the high idle problem by achiving right temp.

Thanks for all your help.

Yeah, It cost money to go to School..
On the four prong , the sensor is actually 2 seperate sensors in one case ..... [ across from one another ] , so a little test is to make sure they both read out the same .....

Yes, they do. I had hope they don't but they do. Good night!!!

somewhat happy to report
 

that the gauge is showing the right Temp again. Ordered a temperature sender ($14 + $6 shipping) and got about 500 ohm at RT. The bad one gave me ~1500 ohm at RT. Upon idling for ~5 minutes, I got 82 C reading.

Anyway, flushed the system with distill water. Replaced a perfectly good T-stat, replaced a bad sender, fill it up with Zerex G-05 coolant and distill water. Total cost of $70 but learnt everthing about the cooling system.

After my tragi-comical adventure with the alternator and the additional removal of radiator, I had to complete the coolant - poured in about 2 liters of pure antifreeze(a local, poor-quality brand). Now it heats up better: 75-80C during driving, 80C or over in stop and go traffic. Guess the "diluted" coolant it previously had(mostly distilled water) made it run colder in the hotter months of the year ....

~Nautilus