In principle you can instantaneously set the throttle opening to some position and set the RPM to whatever you want. In time the RPM will rise or fall until the engine is at equilibrium, but throttle position and RPM aren't like mechanically interlocked. Otherwise how could the engine speed up when you go down a hill?

When you press the gas pedal in your car down (which used to just be a cable to the throttle body), does your car instantaneously increase in speed to match the pedal position?

All you're doing is letting more air in - the RPM is a function of the power the engine generates; more fuel and air than is currently needed for the current load at the current speed = increasing RPMs.

If you put the clutch in, a little blip of the gas is all that's needed to get the RPM quite high very quickly. The moment there's load on there, the same blip will not do very much at all.

Imagine your vehicle is pulling a heavy load up a hill vs. going flat out on a track. Your throttle position may be the same but the RPMs are likely to be quite different, even when you account for the transmission.

> Surely the RPM depends on the throttle?

Partly. Another factor in the equation is load.