Example of how VSS affects Idle Control?

On page 20-2 in the idle air control section it mentions that the vehicle speed sensor is one of the inputs for IAC repositioning. Are there any case studies showing how a faulty VSS might affect idle quality?

hi good question i was just kinda brushing up on idle controls i believe that an rpm signal is needed from crank sensor circuit which gives a more precise data pid of how fast engine is actually turning over

OK, but I don't understand what that has to do with the VSS?

I see where you are headed and am curious myself.

I believe the PCM would use VSS input to effect IAC on deceleration to prevent stalling.

To me the book seemed to imply that it was used at idle also, but maybe I'm reading it wrong.

Maybe if it was some how shorted, not sure if a shorted VR sensor will create a problem like that but maybe a Hall Effect speed sensor using the 5v ref could? Maybe someone can correct me.

I am also thinking of possible AC voltage coming from the alternator on vesicles using VR sensors for VSS since VR sensors create their own AC voltage wave. To much ac voltage could trick the computer into thinking the car is moving, therefore the idle air control system could raise the idle. This could be an effect regardless if there is a IAC Valve or if idle is controlled by the Electronic Throttle Body alone.