When the throttle position sensor (TPS) starts to fail, there are several symptoms that can indicate it needs to be replaced:

1. **Poor Engine Performance**: One of the most common signs of a failing TPS is poor engine performance, such as rough idling, stalling, or surging. The engine may struggle to maintain a consistent speed or respond slowly to throttle input.

2. **Reduced Fuel Efficiency**: A faulty TPS can disrupt the air-fuel ratio in the engine, causing it to consume more fuel than usual. If you notice a sudden decrease in fuel efficiency, it could be a sign of TPS failure.

3. **Difficulty Accelerating**: Another symptom of a failing TPS is difficulty accelerating smoothly. You may experience hesitation or jerking when trying to speed up, especially at lower speeds.

4. **Check Engine Light**: In some cases, a faulty TPS can trigger the check engine light on the dashboard. You should have the vehicle's onboard diagnostics system scanned to retrieve the specific error code related to the TPS.

5. **Transmission Issues**: A failing TPS can also affect the transmission's shifting patterns, leading to rough or delayed gear changes. This can contribute to a lack of power or reduced overall performance.

If you are experiencing any of these symptoms, it is recommended to have a professional mechanic diagnose the issue and replace the throttle position sensor if necessary.