Idle Speed Control Valve

[boscoe99]

At what point is the valve taken out of the engine operation equation?

That is, at some engine RPM is it commanded to close completely by the ECM so that all air flows through the throttle bodies and none through the valve?

Is closure (if this is what happens) based on engine RPM, a TPS value or ???

[fairdeal]

All good questions; I suspect Rodbolt has the answers from his classroom training...

little to no "theory of operation" of the ISC in the few Yamaha service manuals I have;

the Merc F225 has a little:



But then there's this "WTF" tidbit in a Yamaha document I once saw online: