Synonyms of 'tick over'
If an engine or vehicle is idling, the engine is running slowly and quietly because it is not in gear, and the vehicle is not moving.
Her limo waited with its engine idling.
be in neutral
Thesaurus for tick over from the Collins English Thesaurus
If an engine is ticking over , it is running at a low speed or rate, for example when it is switched on but you are not actually using it.