|
It is usual for the ECU to be programmed so that when the car is away from idle, the idle air control valve is opened. It may be you are just picking that up. There can be several reasons for the IACV opening.
One is that it allows what is called "sail on" - the car will maintain speed when the throttle is lifted, and not immediately decelerate rapidly due to engine drag. (My car will do a remarkably good job of maintaining a given road speed down hill on a closed throttle no matter what the incline.)
Another is that it can be used to alter the relationship between accelerator pedal position and the air intake into the engine. That can be used to mask driveability problems and more accurately match the pedal position to a torque demand. It's the poor man's DBW throttle.
Even with modern engine management there will be a HC spike with a rapid throttle shut off, so the IACV is used to damp the change in airflow and reduce the associated exhaust emissions.
It can be used to effectively increase the size of the throttle body and so increase wide open throttle air flow capacity (maximum power).
|