Check if the potentiometer drive lever moves freely: it should turn 90°. Check if the return spring is "sagging".
Connect the tester (in ohmmeter mode) to terminals "A" and "E" of the potentiometer and measure the total resistance, which should be within 1.3-2.5 kOhm.
If the total resistance is not within the specified limits, replace the throttle valve potentiometer 1st chamber.
Cars from 1986 model year
The total resistance of the potentiometer is checked on the car. It should be within 1.4-2.6 k Ohm.