Wide open throttle (WOT) refers to an internal combustion engine's maximum intake of air and fuel that occurs when the throttle plates inside the carburetor or throttle body are "wide open", providing the least resistance to the incoming air. In the case of an automobile, WOT is when the accelerator is depressed fully, sometimes referred to as "flooring it".

At WFOT, manifold vacuum decreases. Ideally, to preserve driveability and fuel economy, manifold vacuum should not fall any lower than 1" (mercury).