90 Quattro 20V (Canada) L5-2309cc 2.3L DOHC (7A) (1989)
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On early 1990 models (produced before March 1990), the idle switch was a separate device with its own harness connector and was mounted on the
throttle body next to the potentiometer. On later models (produced after March 1990), the idle switch and throttle valve potentiometer were incorporated
into a single unit, but the idle switch still has its own harness connector.
SELF DIAGNOSIS-THROTTLE VALVE POTENTIOMETER
The ECU can recognize an open or short in the potentiometer circuit. The signal from the potentiometer is compared with the signals from the idle
switch and the air mass sensor to determine if they agree. If the signals do not agree, or if an open or short circuit is detected, a fault code will be stored.
SELF DIAGNOSIS-IDLE SWITCH
The ECU compares the signal from the idle switch to that of the throttle valve potentiometer and the engine speed sensor, to see if they agree. If the
idle switch remains closed during a changing signal from the potentiometer, a fault code will be stored for the idle switch. Also, if the engine speed
sensor signal is increasing, indicating "off idle" operation and the idle switch remains closed, or if the idle switch does not close at least once within the
first 10 minutes of engine operation, a fault code will be stored for the idle switch.
There is no substitute signal for either the idle switch or throttle valve potentiometer.
