Air Induction

All combustion engines are inherently a sealed unit. With heat build-up when running they will build up pressure internally as the oil is splashed around and sprayed over components to keep them well lubricated. This creates a build-up of vapors in the crankcase and if not vented can internally pressurise the engine and force oil out of seals and gaskets. In the old days this was just vented to the atmosphere.

Since the 70's the PCV valve has done this job. The PCV valve is one way so it lets the pressure out, not the air in. Usually mounted near the top of the engine it connects to the intake manifold. They have done this so oil vapour is sucked out of the crankcase and burned in the combustion process. On older, worn out engines or diesels you may need to put in a filter as they can pump out too much oil vapour which hurts combustion.

Cool or cold air works best in the combustion process as it is denser than warm or hot air. Turbochargers run hot exhaust gas right next to intake air when in operation. This heats the air going to the combustion chamber. To cool it down a good turbo installation will run an intercooler. The intercooler works like a coolant radiator. Hot air enters one end, flows through it and is cooled by airflow going through the intercooler. It comes out the other end cooler and denser which aids combustion.

A throttle bodys main role is to control air flow to the engine. Your accelerator pedal hooks up to it and it has a large round butterfly valve in a tube that when idling is fully closed. When accelerating flat out the butterfly valve is fully open. When closed and the engine is idling, there is a small passage with an adjustable screw for air that bypasses the butterfly valve.

It usually has provisions for a throttle position sensor (butterflies position) and a MAP (Manifold Absolute Pressure) sensor which is located behind the butterfy valve.