Easy to understand guide on how an automotive engine throttle actuator and throttle body with
IAC valve work, this information pertains to most vehicles.
A throttle actuator and throttle body are generally the same part, the actuator
is fully computerized (no cable) with no IAC (idle air control) valve. These devices
control the volume or amount of air that enters the engine via the driver's accelerator
A throttle actuator is held to the intake manifold using three or four bolts
sealed with a gasket, a computer wiring harness connector is directly plugged into
Coolant hoses are used to transfer heat into the actuator to help warm the intake
air for better economy.
Actuator Bolts - Wiring
A condition called "coking" occurs after miles of usage and should be cleaned
to restore the actuator performance. (Coking can cause hard starting, high or low
Throttle Actuator Coolant Lines
A throttle actuator must open and close freely, if rough spots exist in its operation
it must be replaced.
Throttle Actuator Coking
On older vehicles an idle air control (IAC) valve is used to control idle speed
via the computer, there is no adjustments on either style of throttle body configurations.
This design requires a throttle position sensor (TPS) which provides throttle butterfly
position data for the computer.
This idle control uses bypass ports designed onto the throttle bore (idle air
Idle Air Control Valve IAC
A throttle actuator is assembled with tamper proof bolts so it cannot be taken
apart, if this unit fails it must be replaced, never use an actuator that has been
tempered with. The throttle actuator design is sometimes referred to as a "drive-by-wire"
system, which references the absence of a throttle cable directly connected to the
accelerator, drive by wire vehicles use an accelerator position sensor (APS) located
at the pedal arm.
Article first published 2016-02-05