A couple of descriptions. But basically an acceleration pump.
Throttle Switch
The throttle switch can be found mounted underneath the throttle body. To test, turn on the ignition and open the throttle with your hand. You should be able to hear the injectors firing, a sort of "brrrrrrp" noise. If working correctly, the injectors will fire 20 times for the full range of movement. One very mysterious intermittent fault caused by the throttle switch is an occasional "bucking" while driving at constant speed. This is caused by the switch cutting of the fuel and then turning it back on. Test by disconnecting the switch (it is amazing how well the car will run without it, actually), you will notice that acceleration will be a little sluggish as the "accelerator pump" action will be missing.
The throttle valve switch is mounted on the throttle housing. This switch signals the
control unit of throttle position. During deceleration, above 1500 RPM, throttle switch
cuts fuel supply off and below 900 RPM, fuel supply is turned on.
Attached file has more info on around page 14
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