Throttle Body: Description and Operation

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

OPERATION

Airflow Control
- The throttle body controls air flow to the engine through a double-butterfly type valve. The throttle position is controlled by a multi-link, progressive opening, throttle linkage.

- The bypass channel controls both cold and warm engine idle flow as regulated by an Idle Air Control (IAC) valve that is mounted directly to the throttle body. The IAC valve meters airflow around the throttle plate in order to control engine idle speed.

Idle Speed Control
- Base idle speed is controlled by the Powertrain Control Module (PCM) and cannot be adjusted. The traditional idle air adjust procedure is not longer used.

Cold Weather Operation
- Engine coolant is diverted through the throttle body mounting pad to improve cold weather operation.

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.

CAUTION: The throttle body uses a sealant / coating covering the throttle bore and throttle plate that make the throttle body tolerant to engine intake sludge accumulation. There is a yellow / black attention decal on the throttle body stating that the throttle body should not be cleaned.

CONSTRUCTION
- The throttle body housing assembly is a single piece of aluminum. It has a dual bore with an air bypass channel around the throttle plate.