Electronic Idle Speed Control

Idle speed air control valve or idle speed boost valve, located in throttle valve by-pass hose, receives signals from ECU. The ECU uses input from engine speed, the position of the airflow sensor potentiometer and the coolant temperature, to control idle speed.

A/C operation will also send a signal to the ECU which will modify the signal to the air control valve(s). Idle speed boost valves are used on 4-cylinder 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.