[me and my metro]

I would be tempted to add a resistor to the temp circuit to trick the computer. This is the chart out of a 2002 4t40 manual. I would think 400 ohms would do the trick. I did this to the iat and coolant temp sensors a few years ago while playing with a Geo Metro. I could start the car like normal and within 1 mile from cold start I could flip the switch and the car would tolerate warm fuel trims. Put it on a spdt switch so you could make it lock up when you wanted. You will loose the overtemp ability if you lock the temp with a resistor. Verify that this chart is accurate for your car, as always use at your own risk.