Intake Air and Throttle Body System

The intake air system delivers filtered and controlled air flow to the engine. Three groups of components make up the system: air handling, sensors, and control devices.
Intake air system air handling components include the inlet air duct, air cleaner, throttle body (TB), intake manifold, and two resonance chambers. The resonance chambers suppress air inlet noise caused by air flow pulsations. The TB contains the idle speed control (ISC) valve, idle air control (IAC) valve, throttle valve and throttle position (TP) sensor.

Intake air system sensors include a heated resistor-type mass air flow (MAF) sensor and throttle position (TP) sensor; both supply data to the powertrain control module (PCM). The PCM also monitors engine speed.

The idle speed control (ISC) valve compensates for idle speed change caused by the operation of the air conditioner compressor. The ISC valve is energized when the air conditioner clutch is energized.

The idle air control (IAC) valve adjusts the amount of air allowed into the engine at idle condition and during rapid engine deceleration. This adjustment is done by means of an adjustable duty cycle output by the powertrain control module (PCM). The PCM increases the duty cycle based on different inputs such as RPM, load and others.

The idle switch detects idle position when the throttle plate is closed and sends a signal to the powertrain control module (PCM). This signal is sent by the PCM to the transmission control module (TCM) for transmission torque converter clutch control.
• Fuel injection
• Ignition timing
• Fuel pump
• Idle speed

The mass air flow (MAF) sensor is a heated resistor type that indicates to the powertrain control module (PCM) the amount of air being allowed into the engine. The MAF sensor works by trying to keep a resistor at a constant high temperature. The temperature of the hot resistor is referenced with the temperature of a resistor that is held at ambient temperature. As air passes by the heated resistor, the temperature drops and the PCM compensates by allowing more voltage to the MAF. The more air that flows past the heated resistor, the more the temperature will change and cause an increase in required voltage from the PCM. This change in voltage indicates to the PCM that there is more air flowing through the MAF so the PCM can adjust fuel flow, ignition timing, and other outputs.

The throttle body (TB) controls the amount of air that flows into the engine through a single butterfly valve. The single butterfly valve opening is determined by the accelerator pedal. The TB is cast with an air bypass channel and houses several emission-related components for the powertrain control module (PCM).

The throttle position (TP) sensor responds to the accelerator pedal movement. The TP sensor is a  potentiometer that transforms the throttle plate opening angle into output voltage and sends the voltage signal to the powertrain control module (PCM). In addition, the sensor detects the opening and closing speed of the throttle plate and sends the voltage signal to the PCM. Also, the TP sensor is used to determine the air intake when the mass air flow (MAF) sensor fails. This mode of operation is called fail safe.

The TP sensor integrates the idle switch within the housing. The idle switch detects when the throttle plate is closed and an idle condition occurs. The PCM is supplied with this input signal.