Can one say 'throttle up'? The OED only lists 'throttle down':
(throttle back or down) reduce the power of an engine or vehicle by use of the throttle.
Can one say 'throttle up'? The OED only lists 'throttle down':
(throttle back or down) reduce the power of an engine or vehicle by use of the throttle.
I think I will argue that "Throttle up" does not mean "to increase the speed of the vehicle" despite what MacMillan might say. Throttle up definitely means to increase the flow of fuel to the engine, but whether that increase in fuel flow results in an increase in speed is a separate issue- The brakes might still be applied for example.
This is typical in aircraft operations on short runways- the pilot will want to be developing maximum power/thrust prior to starting to move down the runway so he will "throttle up" with the brakes held and only release the brakes once full power has been achieved.
Looking at COCA search results, it doesn't seem to be as common as throttle back but but it is used. Here are some examples:
Endeavour go ahead, throttle up.
Fox (2009) Space Shuttle Launch
GIBBS # Throttle up. Throttle up!
Airforce One (film, Beacon Pictures 1997)
As we throttle up, gaining elevation, the scenery changes as quickly as the canyon ride at Disneyland.
Get Your Motor Running, Forbes (2001)
MacMillan Dictionary defines throttle up as to increase the speed of a vehicle by increasing the supply of fuel to the engine (PHRASAL VERB [INTRANSITIVE]).
So, you can definitely say it with the meaning "accelerate."
See the following Ngram:

"Throttle up" or "Throttle back" is likely to be a checklist item or a command issued by a supervisory pilot or controller to the pilot-flying. As such, "throttle" is not a verb but a noun—the lever or knob that controls engine power—followed by its status, movement, setting, etc. In typical checklist style, the verb—move, set, check, etc.,—is dropped for brevity. I suspect "throttle up" is used instead of "throttle forward" simply because the latter has two syllables instead of one and does not flow as well.
On the other hand, when using "throttle" in conjugated form of a verb with reference to controlling an engine as in "We were throttling back when the engine stalled," the colloquial meaning is to "control using the throttle mechanism" and little or no thought is given as to whether the detail action of the throttle valve involves an airflow restricting action or a relaxing action. So "throttle back" is not considered oxymoronic if it is interpreted as "hold back" on engine power.