Cranking Idle Air Control

A smooth engine start requires there to be an adequate amount of air for the supplied quantity of fuel. Ideally the idle air control (IAC) valve will supply enough air for the car to crank without the driver needing to press the accelerator.

Cranking IAC Base Position

The IAC base position is the percentage of time the valve will be open during cranking. This number will likely be higher than the IAC base position used to idle the car as an excess of fuel is usually injected during cranking.

Cranking IAC Taper Duration (Cycles)

The taper duration controls the quantity of engine rotations for the IAC valve to go from the cranking base position to the idle base position. A high number (over 100) will take longer for the revs to drop to idle once the car cranks over. A lower number will transition quicker but may stumble if the transition completes before the cranking fuel ramps down to a normal level.