UnintegratedCircuit
Part 1 - The Throttle Position Switch
What It Is
The Throttle Position Switch (TPS) is a 'sealed' (more on that later) unit containing two microswitches. These microswitches correspond to the two extremes of throttle position: fully closed (aka: idle) and fully open (aka: wide-open throttle). These two throttle positions in particular are important for the reasons discussed in part 2.​
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These microswitches are actuated by a central 'drum' with a couple of lobes. This drum is driven by the shaft that actuates the throttle plate, which itself is connected indirectly to the throttle cable.
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It should be noted that the Throttle Position Switch mentioned here, is not the same as a Throttle Position Sensor fitted to many more modern cars. The latter is usually a potentiometer or similar device, which provides a continuous analogue output to the Engine Control Unit (ECU), rather than a windowed idle < anywhere-in-between < wide-open output as provided by the Throttle Position Switch. Given that they have the same acronym, there is often some confusion between the two, so vigilance pays when researching on forums etcetera.
What It Looks Like
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As shown above, in Figure 1, the TPS is a black plastic module with the electrical connector on one side, and adjustable mounting lugs on opposing sides. The adjustment allows for variations in throttle cable tension and throttle plate stop position variations. Whilst this project does not cover the optimal adjustment for this unit, how to test it will be explained in a later part.
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It should also be noted that Figure 1 shows the outer face of the module, the recess to accept the throttle plate shaft is on the back of the module, opposite the raised circle in the middle of the unit. The pinout, from left to right, is: wide-open switch, ground, idle switch.
Where It Is Located
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As shown above in Figure 2 (hopefully), the TPS is the black plastic module located right in the centre of photo. It is on the firewall side of the throttle body, which is in turn located towards the rear of the engine bay by the intake manifold (the large U-shaped metal thing). This means it is relatively easy to access should removal be necessary, more information on that procedure can be found in a later part.
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So, now that a bit more is known about the TPS, attention can be focussed on its importance with regards to the operation of the engine.
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