Idle Speed Boost Valves

Idle speed boost valves are used on 4-cylinder Volkswagen models. Vehicles without A/C use only one valve, called Idle Speed Boost Valve No. I. Vehicles with A/C also use second valve, called Idle Speed Boost Valve No. II.

With ignition on, constant voltage is supplied to idle speed boost valve No. I. If engine speed drops below 700 RPM, idle speed boost control (on relay board) completes ground circuit for boost valve No. I. Above 1050 RPM, control unit shuts off ground circuit to boost valve No. I.

Idle speed boost valve No. II is always grounded. When A/C is turned on, voltage is supplied to boost valve No. II.