Peugeot 107 Diesel Engine Stalling

That sounds familiar. I also drive a 107 and experienced very similar symptoms a while back: reduced engine power, rough running, and the check engine light. In my case, it was a malfunctioning fuel injector. Before jumping to conclusions, have you checked the basics? When you say "mixture preparation error", do you mean you used an OBD II scanner to read the error code? What code number did it return? Have you inspected the fuel lines for leaks or damage? A loss of fuel pressure could contribute to the symptoms. How is the idle when the engine is cold, compared to when it's warm?

Yes, I used an OBD II scanner, and the error code pointed towards a mixture preparation error, specifically indicating a potential issue with the fuel injection system. I haven't inspected the fuel lines yet, but I will. The engine idle is more unstable and prone to stalling when the engine is cold, gradually improving as the engine warms up. Does your initial assessment still lean towards a faulty fuel injector, or are there other potential avenues I should explore?

Given the error code and the cold-start idle issue, I still suspect the fuel injector(s). It's possible that one or more of your injectors are clogged, leaking, or not delivering the correct amount of fuel. The fact that the idle improves as the engine warms up suggests that the injectors might be struggling to function optimally when cold. I think you should visit a workshop to test the injection valves. While other components, such as the catalytic converter or oxygen sensor, could be contributing to the problem, the symptoms and error code strongly suggest that the fuel injection system is the primary suspect. I would recommend consulting with a qualified mechanic for a more definitive diagnosis and repair.

Following your advice, I consulted with a trusted mechanic, who confirmed your suspicion of a defective fuel injector. The faulty injector was replaced at a cost of 515€, and the engine now runs smoothly, and the check engine light has been extinguished.