Where is the idle air control 2008 Uplander 3900

Your looking for a part that doesn't exist on your vehicle . Your vehicle has electronic throttle control , DC motor on the throttle body controls the idle speed . Complex electronics an position sensors in both the gas pedal an throttle body are what control the speed of the engine . Your best bet , take it to a qualified repair shop . Without knowledge of these systems an a professional scan tool to view sensor data you shouldn't even try to affect a repair .

The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the driver's intent based on input from the accelerator pedal position sensors, then calculates the appropriate throttle response based on the throttle position sensors. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the throttle actuator motor. The throttle blade is spring loaded in both directions, and the default position is slightly open.

Reduced Engine Power Mode
When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
• Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
• Throttle default mode--The ECM will turn OFF the throttle actuator motor, and the throttle will return to the spring loaded default position.
• Forced idle mode--The ECM will perform the following actions:
- Limit engine speed to idle positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF.
- Ignore the accelerator pedal input.
• Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.

Your engine has an electronic throttle body. They don't use an idle air control valve. They control idle by cracking open the throttle plate electronically. If you have idle problems, chances are you've got carbon buildup around the throttle plate. Here's how to clean it. http://ricksfreeautorepairadvice.com/clean-an-electronic-throttle-body