A "vacuum leak" refers to a situation where air is entering an area where it shouldn't, causing a disruption in the proper functioning of a machine or system that relies on a vacuum or negative pressure.
Sentences with «vacuum leak»
I usually check the engine for vacuum leaks first. (yourmechanic.com)
The car acted like it had a significant vacuum leak in park or at a stop light especially when warm. (mechanics.stackexchange.com)