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Intake Air Systems



Intake Air Systems

Overview

The intake air system provides clean air to the engine optimizes air flow and reduces unwanted induction noise. The intake air system consists of an air cleaner assembly resonator assemblies and hoses. Some vehicles use a hydrocarbon filter trap to help reduce emissions by preventing fuel vapor from escaping into the atmosphere from the intake when the engine is off. It is typically located inside the air intake system. The mass air flow (MAF) sensor is attached to the air cleaner assembly and measures the volume of air delivered to the engine. The hydrocarbon trap is part of the EVAP system. For more information on the EVAP System~ refer to Evaporative Emission (EVAP) Systems in this section. The MAF sensor can be repaired or replaced as an individual component. The intake air system also contains a sensor that measures the intake air temperature (IAT) and which may also be integrated with the MAF sensor. (Refer to Powertrain Control Module (PCM) Inputs for additional information on the MAF and IAT sensors in this section.) Air induction resonators can be separate components or part of the intake air housing. The function of a resonator is to reduce induction noise. The air induction components are connected to each other and to the throttle body assembly with hoses.






There are 3 basic types of intake air sub-systems:

^ Intake Manifold Runner Control (IMRC) electric actuated system
^ Intake Manifold Runner Control (IMRC) vacuum actuated system
^ Intake Manifold Tuning Valve (IMTV)

There are several different styles of hardware used to control airflow within the engine air intake system. In general the devices are defined based on whether they control in-cylinder motion (charge motion) or manifold dynamics (tuning).

Systems designed to control charge motion are defined to be intake manifold runner controls. Intake manifold runner control systems generally have to modify spark when the systems are active because altering the charge motion affects the burn rate within the cylinder.

Systems designed to control intake manifold dynamics or tuning are defined to be intake manifold tuning valves. Intake manifold tuning systems generally do not require any changes to spark or air/fuel ratio because these systems only alter the amount of airflow entering the engine.

These subsystems are used to provide increased intake airflow to improve torque emissions and performance. The overall volume of air metered to the engine is controlled by the throttle body. Vehicles equipped with electronic throttle control (ETC) will not use an idle air control (IAC).

Intake Manifold Runner Control (IMRC) Electric Actuated System

WARNING: SUBSTANTIAL OPENING AND CLOSING TORQUE IS APPLIED BY TillS SYSTEM. TO PREVENT INJURY, BE CAREFUL TO KEEP FINGERS AWAY FROM LEVER MECIIANISMS WIIEN ACTUATED.

The IMRC electric actuated system consists of a remote mounted motorized actuator with an attaching linkage for each housing on each bank. The linkage attaches to the housing butterfly plate levers. Some variations can have either 2 intake air passages for each cylinder with one passageway that is always open and the other is opened and closed with a butterfly valve plate. The other type has a butterfly valve with a small passageway that opens up into a larger size orifice when the butterfly plates are opened. The butterfly valve plates are opened and closed by an electric motor and the motorized actuator houses an internal switch or switches depending on the application to provide feedback to PCM indicating the butterfly valve plate position. If the IMRC system is not working correctly then a DTC will be set.

Below approximately 3OOO RPM the motorized actuator will not be energized. This will allow the linkage to fully extend and the butterfly valve plates to remain closed. Above approximately 3OOO RPM the motorized actuator will be energized. The attaching linkage will pull the butterfly valve plates into the open position. Some vehicles will activate the IMRC near 15OO RPM.

1. The PCM uses the throttle position (TP) sensor and crankshafi position (CKP) signals to determine activation of the IMRC system. There must be a positive change in voltage from the TP sensor along with the increase in RPM to open the valve plates.

2. The PCM uses the information from the input signals to control the IMRC motorized actuator based upon RPM and changes in the throttle position.

3. The PCM energizes the actuator to open the butterfly plates.

4. The IMRC housing contains butterfly plates to allow increased air flow.






Intake Manifold Runner Control (IMRC) Vacuum Actuated System

WARNING: SUBSTANTIAL OPENING AND CLOSING TORQUE IS APPLIED BY TillS SYSTEM. TO PREVENT INJURY, BE CAREFUL TO KEEP FINGERS AWAY FROM LEVER MECIIANISMS WIIEN ACTUATED.

The IMRC vacuum actuated system consists of a manifold mounted vacuum actuator and a PCM controlled electric solenoid. The linkage from the actuator attaches to the manifold butterfly plate lever. The IMRC actuator and manifold are composite/plastic with a single intake air passage for each cylinder. The passage has a butterfly valve plate that blocks a large percentage of the opening when actuated leaving the top of the passage open to generate turbulence. The housing uses a return spring to hold the butterfly valve plates open. The vacuum actuator houses an internal monitor circuit to provide feedback to the PCM indicating the butterfly valve plate position.

Below approximately 3OOO RPM the vacuum solenoid is energized. This allows manifold vacuum to be applied and the butterfly valve plates to remain closed. Above approximately 3OOO RPM the vacuum solenoid is de-energized. This allows vacuum to vent from the actuator and the butterfly valve plates to open.

1. The PCM monitors the TP sensor CHT and CKP signals to determine activation of the IMRC system. There must be a positive change in voltage from the TP sensor along with the increase in RPM at the proper engine temperature to open the valve plates.

2. The PCM uses the information from the input signals to control the IMRC electric solenoid based upon changes in the throttle position the engine temperature and the RPM.

3. The PCM energizes the solenoid with the key on and the engine running. Vacuum is then applied to the actuator to pull the butterfly plates closed.






Intake Manifold Tuning Valve (IMTV)

WARNING: SUBSTANTIAL OPENING AND CLOSING TORQUE IS APPLIED BY TillS SYSTEM. TO PREVENT INJURY, BE CAREFUL TO KEEP FINGERS AWAY FROM LEVER MECIIANISMS WIIEN ACTUATED.

The IMTV is a motorized actuated unit mounted directly to the intake manifold. The IMTV actuator controls a shutter device attached to the actuator shafi. There is no monitor input to the PCM with this system to indicate shutter position.

The motorized IMTV unit is not energized below approximately 26OO RPM. The shuffer is in the closed position not allowing airflow blend to occur in the intake manifold. Above approximately 26OO RPM the motorized unit is energized. The motorized unit is commanded on by the PCM initially at a 100 percent duty cycle to move the shutter to the open position and then falling to approximately 50 percent to continue to hold the shutter open.

1. The PCM uses the TP sensor and CKP signals to determine activation of the IMTV system. There must be a positive change in voltage from the TP sensor along with the increase in RPM to open the shutter.

2. The PCM uses the information from the input signals to control the IMTV.

3. When commanded on by the PCM the motorized actuator shutter opens up the end of the vertical separating wall at high engine speeds to allow both sides of the manifold to blend together.






Throttle Body System Overview

Note: This overview is for applications without electronic throttle control (ETC). For ETC applications refer to Torque Based Electronic Throttle Control (ETC) in this section.

The throttle body system meters air to the engine during idle part throttle and wide open throffle (WOT) conditions. The throttle body system consists of an idle air control (IAC) valve assembly an idle air orfice single or dual bores with butterfly valve throttle plates and a throttle position (TP) sensor. One other source of idle air flow is the positive crankcase ventilation (PCV) system. The combined idle air flow (from idle air orifice IAC flow and PCV flow) is measured by the MAF sensor on all applications.

During idle the throttle body assembly provides a set amount of air flow to the engine through the idle air passage and the PCV valve. The IAC valve assembly provides additional air when commanded by the PCM to maintain the proper engine idle speed under varying conditions. The IAC valve assembly mounts directly to the intake manifold assembly in most applications. Idle speed is controlled by the PCM and cannot be adjusted.

Note: The traditional idle air adjust procedure and the throttle return screw are no longer used on OBD applications.

Throttle rotation is controlled by a cam/cable linkage to slow the initial opening rate of the throttle plate. The TP sensor monitors the throttle position and provides a signal to the PCM. Some throffle body applications provide an air supply channel upstream of the throffle plate to provide fresh air to the PCV or IAC systems. Other throffle body applications provide individual vacuum taps downstream of the throttle plate for PCV return exhaust gas recirculation (EGR) evaporative emission (EVAP) and miscellaneous control signals.

Throttle Body System Hardware

The major components of the throttle body assembly include the TP sensor the IAC valve assembly and the throttle body housing assembly.

Throttle Position (TP) Sensor

The TP sensor monitors the throttle position and provides an electrical signal to the PCM. It is monitored by the OBD system for component integrity system functionality~ and faults that can cause emissions levels to exceed the standards set by government regulations.

Idle Air Control (IAC) Valve (Applications Without ETC)

The IAC valve assembly controls the engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine RPM and increases or decreases the IAC duty cycle in order to achieve the desired RPM.

Note: The IAC valve assembly is NOT ADJUSTABLE and CANNOT BE CLEANED also some IAC valves are normally open and others are normally closed. Some IAC valves require engine vacuum to operate.

The PCM uses the IAC valve assembly to control:

^ No touch start.
^ Cold engine fast idle for rapid warm-up.
^ Idle (corrects for engine load).
^ Stumble or stalling on deceleration (provides a dashpot function) Over-temperature idle boost.

Throttle Body Housing

The throttle body housing assembly is a single piece aluminum or plastic casting with an air passage and a butterfly throttle plate with linkage mechanisms. When the throttle plate is in the idle (or closed) position the throttle lever arm should be in contact with the throttle return stop. The throttle return stop prevents the throttle plate from contacting the bore and sticking closed. The seffing also establishes the amount of air flow between the throttle plate and bore. To minimize the closed plate air flow 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 of the Throttle Body Assembly include:

1. Idle air control (IAC) valve assembly mounted directly to the throttle body assembly (some vehicles).

2. A pre-set stop to locate the WOT position.

3. An air supply channel upstream of the throttle plate to provide fresh air to the PCV system (some vehicles only).

4. Individual vacuum taps for PCV EGR EVAP and miscellaneous control signals (some vehicles only).

5. PCV air return (if applicable).

6. A throttle body-mounted TP sensor.

7. A sealant/coating on the throffle bore and throttle plate makes the throttle body air flow tolerant to engine intake sludge accumulation. These throttle body assemblies MUST NOT BE CLEANED and have a white/black attention decal advising not to clean.

8. A non-adjustable stop screw for close plate idle air flow.