The throttle position sensor (TPS) on the 2008 Chevrolet Trailblazer and Trailblazer LT is known for failure which causes:

This issue is related to the throttle position sensor, and can be caused by faulty wiring to the TPS, bad connection at the TPS, or a failed TPS.

To correct this issue, the wiring harness, connector, and throttle position sensor must be inspected, tested, and/or replaced. The most common cause is a faulty TPS.