The exception is monopoint or TBI injection systems which spray fuel onto the throttle plate.

This prevents ice from forming around the throttle plate but does not draw large amounts of hot air into the engine as carburetor heat does.

This ice forms on the throttle plate, which is located "down stream" of the fuel nozzle.

Each bore contains a number of throttle plates which are used by the pilot to control the air flow into the engine.

A blowoff valve is connected by a vacuum hose to the intake manifold after the throttle plate.

Most Diesel engines have no use for a blow off valve as they do not have a throttle plate.

Regardless, it allowed the use of very large throttle plates seamlessly over a very wide engine operating range.

The prefix always indicates the size of the throttle plate.

In petrol engines, instead, vacuum is obtained as a side-effect of the operation of the engine and the flow restriction created by the throttle plate.

With the throttle retarded to avoid overboosting, air temperature in the carburetor can drop low enough to cause ice to form at the throttle plate.