the.com/idling
An engine running just to prove it still can, going nowhere expensively.
means Keeping something operating at minimum activity without doing useful work, especially an engine left running while stationary.
from From Old English idel, meaning empty, useless, or worthless — the word for laziness quietly became the word for machines wasting fuel.
Fuel costIdling burns up to half a gallon hourly.
IllegalMany cities cap idling at a few minutes.
Auto-stopModern cars kill the engine to dodge it.