switches is easy: unplug the LH and take measurements with a multi meter at pin
2 to ground and 3 to ground. Then engage the pedal and press until WOT. You should see a idle contact and a WOT contact making ground.
1988 928s4 cherry red
Theo wrote the pins to check for the idle switch. You need to make sure it is
reliably changing state between when you are not touching the gas pedal and when
just barely pressed. Use your hand to press lightly. On my car the idle switch
would become erratic, only when the engine was warm - so test it when the
problem is occurring.