Idle Stabilization System

From VanagonWiki

The idle stabilization system works in parallel with the ECU (Engine Control Unit).

While the gas pedal is pressed, fuel injection and sometimes also ignition depending on the system installed are controlled by the ECU, but once the gas pedal is released, the Idle Stabilization System takes control over setting the motor idle speed, to keep it from stalling or running too fast (also affects polution), as well as taking into account additional variable loads such as Power steering (heavier load while turning) and Air Conditioning, again to prevent the motor from stalling.

1983.5 - 1985 Vanagons have a "Digijet" ECU that controls only fuel injection (Ignition is separate and controlled by the Hall sender inside the distributor + ignition coil driver circuitry). They have a FIRST type of Idle Stabilization System that controls idle by modifying ignition timing. The control module is mounted in front of the ignition coil.

1986 - 1991 Vanagons have a "DigifantECU that controls both fuel injection and ignition, and a SECOND type of Idle Stabilization System that controls idle by modulating an Idle Control VALVE ICV that bypasses air around the throttle valve. The ICV is mounted on top of the motor (center) while the Idle Stabilization Control Unit ISCU is mounted hidden behind the rear right tail-lights.

European versions are a bit different: the "Digijet" ECU (without integrated ignition control) was used throught (1983.5 - 1991) and without Catalytic converter. In 1986 the Idle Stabilization System changed to the 2nd type. 1983.5 - 1985 engines were 2000cc 4 speed gears (or automatics), while 1986 - 1991 were 2100cc, often with 5 speed manual gears (or automatics).