Usually the throttle valve is controlled with a throttle pedal or lever via a direct mechanical linkage.
From the en.wikipedia.org
The other tube has a throttle valve on the end.
From the newscientist.com
A physical spring should close a physical throttle valve when the driver releases the gas pedal, no matter what is happening in the electronics.
From the economist.com
Until recently, even with computerized engine controls, a physical cable or linkage connected the gas pedal to the throttle valve in the engine's air intake.
From the economist.com
The valve had been opened to full throttle, according to city fire investigators.
From the sacbee.com
On the steering column is the hand throttle, next to yet another valve.
From the washingtontimes.com
On the flip side, full throttle openings reduce friction at that valve.
From the economist.com
But, when you suddenly stamp on the throttle, the valve will open again in that same intake stroke and much more fuel will be injected so that you start to accelerate immediately.