What is the function of an engine's intake system?

Intake system components: (1) AIR INTAKE — opening at the front of the engine bay; modern designs are 'cold air intakes' drawing from cooler areas (denser air = more power); (2) AIR FILTER — paper or oiled gauze filter; traps dirt, dust, debris; replace per maintenance schedule (typically 15,000-30,000 miles, or sooner in dusty conditions); essential — engines breathe enormous volume of air (a 2.0L engine at 3000 RPM ingests over 3000 L of air per minute); even small particles damage engines; (3) MASS AIRFLOW SENSOR (MAF) or MANIFOLD ABSOLUTE PRESSURE SENSOR (MAP) — measures airflow into engine; ECU uses this to calculate proper fuel injection amount; MAF measures airflow directly with a heated wire; MAP measures vacuum in intake manifold (correlates with airflow); both critical to engine operation, faulty sensor → incorrect fueling → poor running; (4) INTAKE AIR TEMP SENSOR (IAT) — air temperature affects density; cold air is denser (more mass per volume) so requires more fuel; sensor allows fueling adjustment; (5) THROTTLE BODY — contains THROTTLE PLATE (butterfly valve) that controls airflow into engine; on gasoline engines, throttle position determines engine power (more throttle = more air, ECU adds more fuel proportionally); modern cars use DRIVE-BY-WIRE/ETC (Electronic Throttle Control): no mechanical link from pedal to throttle, pedal sends electronic signal to ECU which positions throttle motor; allows traction control, cruise control, stability control intervention; (6) THROTTLE POSITION SENSOR (TPS) — tells ECU current throttle position; (7) INTAKE MANIFOLD — distributes air from throttle body to each cylinder; usually plastic or aluminum; runners (passages to each cylinder) are tuned in length and shape to optimize airflow at specific RPM ranges; some modern engines have VARIABLE-LENGTH INTAKE RUNNERS that change for low-end vs high-end power; (8) IDLE AIR CONTROL valve (older systems) — bypasses throttle plate at idle to maintain idle RPM; modern systems do this with throttle plate control directly. AIR-FUEL RATIO: stoichiometric (chemically balanced) for gasoline = 14.7 parts air to 1 part fuel by mass. ECU varies this: 12-13:1 for power (rich, more fuel for cooling and complete combustion under load); 14.7:1 for cruise (efficient, meets emissions); 16-18:1 for max fuel economy in some conditions (lean burn). RICH = more fuel (black smoke, poor economy, fouled plugs, increased emissions); LEAN = less fuel (white/blue exhaust possible, hot combustion, ping/knock risk, possible damage if extreme). FORCED INDUCTION: TURBOCHARGER uses exhaust gas to spin a turbine which spins a compressor that forces more air into engine; SUPERCHARGER does the same but driven mechanically by the engine; both INCREASE air mass = more power output for given engine size. INTERCOOLER: cools the compressed air before it enters engine (compression heats air; cooler air is denser); typically air-to-air or air-to-liquid. Boost pressure: how much above atmospheric (psi or bar); modern: 6-30 psi typical; race: higher. CRANKCASE VENTILATION: PCV (Positive Crankcase Ventilation) valve allows blowby gases (combustion gases that leak past piston rings into the crankcase) to be drawn back into intake and burned; reduces emissions and prevents pressure buildup in crankcase. EVAP system: captures fuel tank vapors in CHARCOAL CANISTER, releases them into intake when engine running, prevents fuel vapor emission to atmosphere.