G 3500 1 Ton Van V8-454 7.4L VIN N TBI (1995)
This movement controls airflow around the throttle plate, which in turn, controls engine idle speed, either cold or hot. IAC valve pintle position
counts can be seen using a Tech 1 scan tool. Zero (0) counts correspond to a fully closed passage, while 140 counts or more (depending on the
application) corresponds to full flow.
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Actual or "controlled" idle speed is obtained by the control module positioning the IAC valve pintle. Resulting idle speed is generated from the
total idle air flow (IAC/passage + PCV + throttle valve + vacuum leaks).
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Controlled idle speed is always specified for normal operating conditions. Normal operating condition is engine coolant temperature in
operating range, the A/C is "OFF," manual transmission is in neutral or automatic transmission in drive with proper park/neutral position. A
high or low engine coolant temperature, or A/C clutch engagement may signal the control module to change the IAC counts.
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The minium idle speed is set at the factory with a stop screw. This setting allows enough air flow by the throttle valves to cause the IAC valve
pintle to be positioned a calibrated number of steps (counts) from the seat during normal controlled idle operation.
The IAC counts will be higher than normal on an engine with less than 500 miles, or an engine operating at high altitude or an engine with an
accessory load such as the alternator, A/C, power steering or hydra.boost brakes activated.
IDLE SPEED CONTROL ACTUATOR
The idle speed control actuator system assists the idle air control system in controlling the idle speed, primarily at cold temperatures. The idle
speed control actuator is a vacuum operated device which opens the throttle slightly (2 to 3 degrees of angle) to increase the cold engine idle
speed, to improve the mixing of the air and fuel, and to allow lower warmed up engine idle speeds. The idle speed control actuator is controlled by
the idle speed control actuator solenoid, which is controlled by the control module. To increase the idle speed, the solenoid is turned "OFF," and
no vacuum is routed to the idle speed control actuator, allowing it to open the throttle slightly. To decrease the idle speed, the solenoid is turned
"ON" and vacuum is routed through the solenoid to the idle speed control actuator, allowing the throttle to fully close.
In conjunction with the idle speed control actuator system, the idle air control continuously monitors and controls the engine idle speed to the
desired idle speed. A Tech 1 scan tool will read the control module commands to the idle speed control actuator system.
THROTTLE POSITION (TP) SENSOR
The Throttle Position (TP) sensor is connected to the throttle shaft on the throttle body unit and is non-adjustable. It is a potentiometer with one
end connected to 5 volts from the control module and the other to ground. A third wire is connected to the control module to measure the voltage
from the TP sensor.
As the throttle valve angle is changed (accelerator pedal moved), the output of the TP sensor also changes. At a closed throttle position, the output
of the TP signal is low (approximately 0.5 volt). As the throttle valve opens, the output increases so that, at Wide Open Throttle (WOT), the
output voltage should be approximately 4.5 volts.
By monitoring the output voltage from the TP sensor, the control module can determine fuel delivery based on throttle valve angle (driver
demand).
