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Idle Air Control Valve - Engine Braking
IDLE AIR CONTROL VALVE - ENGINE BRAKING During engine braking and at Closed Throttle Position (
CTP), the
Engine Control Module (
ECM) controls the Idle Air Control (
IAC) Valve so that air is supplied to the engine to:
^ maintain the negative pressure in the inlet manifold within bounds
^ improve combustion and reduce emissions
^ control engine braking and how fast engine speed can drop.