Idle air control at base of throttle body. Passages could be plugged or idle hard stop needs adjusting.
Air Intake System Sensors
Air intake 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.
Air Intake System Control Devices
The idle air control (IAC) solenoid regulates idle speed by adjusting the amount of air allowed into the intake manifold. Adjustment is made by varying the duty cycle output by the powertrain control module (PCM). The PCM will increase the duty cycle for added mechanical or electrical loads. The IAC solenoid is combined with the fast idle control (FIC) solenoid which is turned on when the air conditioner is engaged to help compensate for the additional load. The IAC valve must be replaced as an assembly with the FIC solenoid.
Fast Idle Control (FIC) Solenoid
The fast idle control (FIC) solenoid (Figure 1) compensates for idle speed change caused by the operation of the air conditioner compressor. The FIC solenoid is controlled by the FIC relay. The FIC relay is energized when the air conditioner clutch is energized and the relay allows the FIC solenoid to turn on and let an additional volume of air into the intake manifold.
Figure 1: Fast Idle Control (FIC) Solenoid
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Throttle Body (TB)
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).
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Throttle Position Sensor (TP Sensor)
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 (IDL) switch within the housing. The IDL switch detects when the throttle plate is closed and an idle condition occurs. The PCM is supplied with this input signal.
IDLE SPEED
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