Idle Speed
WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
PCM controls engine idle speed depending upon engine operating conditions. PCM senses engine operating conditions and determines best idle speed. Idle speed is controlled through Throttle Actuator Control (TAC) system. If engine idle speed is out of range for a calibrated period of time, an idle speed related DTC will set. To diagnose, perform related diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article.