The TPS is a simple potentiometer AKA variable resistor. You find them commonly in old stereos, etc as volume controls. They can and do go bad. Most of the time the contact points on the wiper arm get dirty, stop smoothly transitioning from one resistance to another. In an old stereo you would hear it as static and popping when you turned the knob. Sometimes they can be cleaned (electrical contact cleaner), sometimes they can't. Sometimes they fail open, or at a particular resistance, appearing to be stuck even though they turn freely.
To troubleshoot one simply hook up a multimeter and measure the resistance while rotating the TB shaft. With the throttle plate closed it should measure around 1K ohms. When fully open it should be about 5K ohms. The transition should be smooth. They are easier to read with an analog meter because you can see the needle moving smoothly.
TPS adjustment and test
From the DSM VFAQ site: