idling speed

plural idling speeds

1. The speed, measured in revolutions per minute, of an internal-combustion engine when it is running, but is at rest and without power being applied, typically with transmission in neutral.

   1 more example

   Heating in the passenger sections is by electricity obtained from the main generator. When heating is dictated by the operation of a thermostat in the roof of the motor coach, engine idling speed is 600 r.p.m. instead of the normal 450 r.p.m. in order to produce a high enough generator voltage output at rest.

   1962 December, “The Oxted Line diesel-electric multiple-units”, in Modern Railways, page 383