Idle Speed & Ignition Timing
WARNING: This page does not describe the selected car, but rather 21 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Savana Special. However, it is still accessible from the selected car via links, so may be relevant.
Idle speed and ignition timing are controlled by PCM. Incorrect idle speed are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.