Throttle sensor MERCEDES-BENZ A-Class (W176)

Based on your description of a throttle position sensor fault on your 63 plate class vehicle that's entering limp mode, I can help identify what might need replacing.

The issue you're experiencing is likely related to the throttle position sensor (TPS) system. Since you've already replaced the throttle pedal (which contains the accelerator pedal position sensor), the problem might be with the throttle body itself or the throttle position sensor located on it.

Possible Parts Needed

Throttle Body/Throttle Position Sensor
The throttle position sensor works in conjunction with the accelerator pedal position sensor, and the ECU expects these two sensors to correlate properly. When they don't, fault codes like P2138 can be triggered, which puts the vehicle into limp mode. Since you've already replaced the pedal, the throttle body or the TPS mounted on it is the next likely culprit.

Wiring Harness
Before replacing parts, check the wiring connections between the throttle body and the ECU. Loose, damaged, or corroded wiring can cause communication issues between these components. Inspect the 6-pin wiring harness that connects to the throttle position sensor for any visible damage.

Cleaning Before Replacing
Before purchasing a new part, try cleaning the throttle body if it's dirty. Carbon buildup on the throttle body can interfere with the proper operation of the throttle position sensor. Use a throttle body cleaner and carefully clean away any buildup.

If cleaning doesn't resolve the issue, you'll likely need to replace the throttle body assembly or just the throttle position sensor, depending on your specific vehicle model. For most modern vehicles, the throttle position sensor is integrated into the throttle body and sold as a complete unit.

Remember that after replacing the throttle body or TPS, some vehicles require a relearn procedure to calibrate the new sensor with the ECU. This might involve a specific idle relearn procedure or simply driving the vehicle normally for the computer to adapt.