P0171 Mercedes-Benz -

Question

The code P0171 appeared. The garage has changed the O2 sensor, the light is still on.
The idle speed is more stable but still occasionally goes up or down.

Answer 1

HI there,

This sounds like a possible intake manifold gasket leaking. This would cause a lean code on only one side of the engine. I would also check the other O2 sensor. If the shop replaced the rear sensor, it is still possible the front one is causing the code.