Fiat Doblo Throttle Response Fails While Driving

I have been experiencing a problem with my 2004 Fiat Doblo 1.9 JTD for about 20 days, and it is also concerning from a safety standpoint. When the vehicle is idling, there is no issue at all—the engine runs smoothly. The problem only occurs while the vehicle is in motion. While driving, especially on slight inclines and uphill roads, the car loses throttle response, hesitates, and suffers a noticeable loss of power. Sometimes the car drives normally for kilometers without any problem, and other times it suddenly stops responding to the accelerator. This situation not only disrupts my driving comfort but also makes me anxious due to the risk of breaking down on the road.

When I first took the car in, the issue was diagnosed as a faulty accelerator pedal, and a new pedal was installed. However, there was absolutely no improvement afterward. Since the day I bought the vehicle, I have always taken it to the same private service center in İskenderun and had it maintained by the same mechanic, yet despite this ongoing and recurring issue, no clear diagnosis has been made and no solution has been found.

I am requesting technical guidance and professional support from Fiat, especially if there are known or common issues with similar models. In order to resolve this malfunction safely and permanently, I would also like to be informed about how authorized service centers typically handle complaints of this type, if necessary. I ask that my issue be taken seriously and addressed with proper technical attention.