Throttle Body: Description and Operation

Throttle Body Components:

PURPOSE
The throttle body system meters air to the engine during idle, part throttle, and wide open throttle conditions.

CONSTRUCTION
The throttle body system consists of an Idle Air Control (IAC) valve assembly, throttle plate idle air orifice, single or dual bores with butterfly valve throttle plates and Throttle Position (TP) sensor.

OPERATION

Idle Speed Control
During idle, the throttle body assembly provides a set amount of air flow to the engine through the idle air trim screw passage or throttle plate idle air orifice and PCV valve.

GThe IAC valve assembly provides additional air when commanded by the Powertrain Control Module (PCM) to maintain the proper engine idle speed under varying conditions. The idle speed is controlled by the PCM and cannot be adjusted.

Other Features Of The Throttle Body Include:

1. Idle Air Control Valve.

2. Idle Air adjust needle (trim screw) and tamper proof throttle return screw (some models only).

3. A throttle return screw to set the throttle plate at the minimum idle airflow position (factory set and not adjustable on some models.

4. A pre-set stop to locate the Wide Open Throttle (WOT) position.

5. An air supply channel upstream of the throttle plate to provide fresh air to the Positive Crankcase Ventilation (PCV) valve system. (some models only).

6. Individual vacuum taps for PCV, Exhaust Gas Recirculation (EGR), Evaporative Emission (EVAP) and miscellaneous control signals (some models only).

7. A throttle body mounted throttle position sensor.