Throttle Body: Description and Operation

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


CONSTRUCTION
The throttle body housing assembly is a single piece of aluminum casting with an air passage and a butterfly throttle plate with linkage mechanisms.

OPERATION
When the throttle plate is in the idle (or closed) position, the throttle lever arm should be in contact with the Throttle Return Control (TRC) screw. This TRC screw is factory set to provide the minimum throttle plate position and SHOULD NOT BE ADJUSTED. The TRC screw prevents the throttle plate from contacting the bore and sticking closed. The setting also establishes the amount of airflow between the throttle plate and bore. To minimize the closed plate airflow amount, a special coating is applied to the throttle plate and bore to help seal this area. This sealant / coating also makes the throttle body resistant to engine intake sludge accumulation.

FEATURES
The throttle body system consists of an Idle Air Control (IAC) valve assembly, throttle plate idle air orifice, a single bore with butterfly valve throttle plates, and a Throttle Position (TP) sensor. An additional source of idle air flow is the Positive Crankcase Ventilation (PCV) System. The combined idle air flow (from trim screw passage/throttle plate orifice, IAC flow and PCV flow) is measured by the Mass Air Flow (MAF) sensor.

Additional features include:
- Idle air trim screw and tamperproof Throttle Return Control (TRC) screw (some models only). Do NOT adjust.
- A Throttle Return Control (TRC) screw to set at the throttle plate minimum idle airflow position (non-trim screw models only), and SHOULD NOT BE ADJUSTED.
- A preset stop to locate the Wide Open Throttle (WOT) position.
- An air supply channel upstream of the throttle plate to provide fresh air to the PCV system (some models only).
- Individual vacuum taps for PCV, EGR, EVAP and miscellaneous control signals (some models only).
- PCV air return (if applicable).
- A sealant/coating on the throttle bore and throttle plate makes the throttle body airflow tolerant to engine intake sludge accumulation.

NOTE: These throttle body assemblies MUST NOT BE CLEANED and have a white/black attention decal advising not to clean.