I've gone through 3 air temp sensors, and still get negative readings
 

Yep, they are still reading -24 C at startup, and as the car gets warm, this value increases to about -14 C or so, totally inaccurate.

I checked my wiring on the sensor, several times.

Could this situation cause me to run rich?

are you using stock sensors or GM sensors?

I'm using the stock air temp sensors. The last two I used were confirmed working on another car.

try a GM one, for some reason your ecu may be setup to use one of them, the GM one will read higher than the stock mazda one

I have a similar problem as well, but always assumed that it was a faulty sensor.

Since I have a custom intake manifold, trying out a GM sensor may be inconvenient.

What is involved in having the ECU corrected? Does it need to go back to Microtech?

yes it will need to go back to microtech,

just plug one in and see if it reads right

Well, that's just great lol.

Well, this car's not gonna be off the road for some time, what difference would the air temp sensor make in terms of drivability/performance?

just get a GM one and put it in your intercooler pipe and extend the wires, will take about 20min to fit and your problems will be gone,

it wont make a huge difference when your tune is dialed in

Yeah, that's my next plan.