Performance and Fuel Economy Issue

[dfwaltima]

OK, i recently got an s13 and im having some issues with it. I have tested a few things and well this might get a lil long.

The car right now is wasting crazy amounts of gas, and when say crazy i mean like 200 miles to the tank type crazy and this is driving at 3k RPM and shifting no higher than 3k. So i hooked up a scaner to it, o2 reading is between .2 and .8, so thats good. The Engine/Coolant Temp however doesnt seem to want to go up pass 176deg, yesterday i started the car and it was at 176deg the whole time, then poked around, check the sensor, found that the sensor was unplugged, plugged it back in, so now i start the car, i go from 145deg to 176deg in about 15 to 20 mins. Now, i was advised that the temps are to be around 200deg, so i check the sensor, i have good resistance, the temp housing was about 131deg and i got about 616ohm when testing for resistance. Then i tested from the plug to the ecu, well i got .2ohm, so those 2 check out fine. the teacher suggested that it could be a bad ecu stuck on the 176deg "safe" mode and that is affecting the gas milage due to the ecu reading the incorrect temps and setting the incorrect fuel setting.

So, do you guys have any other ideas that i can try, or if anything can help me confirm that this is indeed the problem, i dont feel like buying an ecu, well i dont know the prices for it.

the car is 91 240SX-LE Model, KA24DE