The Throttle Position Sensor (or "TPS") is an integral part of any electronically-controlled fuel system, even many carbureted systems. It is usually attached to one side of the butterfly valve which admits air into the intake manifold, while the throttle linkage is attached to the other. In carbureted systems, the throttle linkage may also have other functions; in fuel injected systems, it is the throttle position sensor which instructs the car as to how much fuel you are attempting to burn.
This is a Delphi Throttle Position Sensor that I purchased from autopartswarehouse.com.
As I may have mentioned previously, my 1993 Subaru Impreza LS has a faulty throttle position sensor. I diagnosed it using a non-autoranging digital multimeter on the megohms setting. A better solution is to use an analog ohmmeter, or to follow the factory test procedure and connect a voltmeter to some of the pins on the ECU. So far so good. I ordered a cheap Delphi replacement part from autopartswarehouse.com, and the fun began.