You can also check the MAT sensor resistance with an Ohm meter. Unplug the wires, and probe the two terminals. Then compare to the chart above. It should correspond roughly to the ambient air temperature.
I had to replace the MAT sensor on my V6 once, because the reading was WAY high. We're talking sensor readings around 140°F, when it's only in the low 70s outside (cold engine). That made the engine run lean, which made it surge and sometimes stall when idling. The bad behavior happened mostly when the engine was cold, because the O2 sensor wasn't active yet.
[This message has been edited by Blacktree (edited 05-18-2014).]