Difference Between Mechanical Air Valves and ECU Controlled ISCV

The ECU controlled ISC systems addressed in this chapter should not be confused with the mechanical air valves which were addressed in Chapter 2, "Air Induction System." The ISC valve is totally controlled by the ECU based on inputs received from the various sensors, and it controls many different idle speed parameters.

The Wax type and Bi-metal mechanical air valves are used only to regulate cold engine fast idle and are not ECU controlled.

There are some engines which utilize a mechanical air valve, for cold fast idle control, in combination with an ECU controlled ISC Vacuum Switching Valve (VSV) to control warm curb idle.

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