The throttle position sensor (TPS) is used with feedback carburetion and electronic fuel injection (EFI) to inform the computer about the rate of throttle opening and relative throttle position. A separate idle switch and/or wide open throttle (WOT) switch may also be used to signal the computer when these throttle positions exist.

The throttle position sensor may be mounted externally on the throttle shaft (the case on most fuel injection throttle bodies), or internally in the carburetor (as in Rochester Varajet, Dualjet and Quadrajet).

The TPS is essentially a variable resistor that changes resistance as the throttle opens. It is the electronic equivalent of a mechanical accelerator pump. By signaling the computer when the throttle opens, the computer enriches the fuel mixture to maintain proper air/fuel ratio.

Initial TPS setting is critical because the voltage signal the computer receives tells it the exact position of the throttle. Initial adjustment must be set as close as possible to factory specs. Most specs are given to the nearest hundredth of a volt.

The classic symptom of a defective or misadjusted TPS is hesitation or stumble during acceleration. The fuel mixture leans out because the computer doesn't receive the right signal telling it to add fuel as the throttle opens. The oxygen sensor feedback circuit will eventually provide the necessary information, but not quickly enough to prevent the engine from stumbling.

When the sensor is replaced, it must be adjusted to the specified reference voltage. The TPS on most remanufactured carburetors is preset at the factory to an average setting for the majority of applications the carburetor fits. Even so, the TPS should be reset to the specific application upon which it is installed.