The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and
eliminates the need for mechanical cable. The TAC system performs the following functions:

•  Accelerator pedal position (APP) sensing
•  Throttle positioning to meet driver and engine demands
•  Throttle position (TP) sensing
•  Internal diagnostics
•  Cruise control functions
•  Manage TAC electrical power consumption

The TAC system includes the following components:
•  The APP sensors
•  The throttle body assembly
•  The powertrain control module (PCM)

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Electronic Throttle Control Description
Bob said:
2004 envoy, 4.2l, engine idle is running very fast , throttle body is spotless. idles at 2000rpm at 30kph.

Stan said:
Reply @Bob, If the throttle is spotless because you just cleaned it, and NOW it idles high, you would need to have the idle relearned. This is best done
with a scanner, but can be done by driving on expressway for a few miles, then letting idle in gear for a few minutes. If this is not the case, then look for
a vacuum leak. The intake manifold bolts tend to get loose.