Hello how are you? What I tell you does not know if it will serve as a comfort or will help you.
I have the same car as you, a 1.4 tdci party. Returning from the field I began to make this erro that you say. It stops, as it runs out of fuel, and after walking, but reaching a certain speed stays.
At the beginning I did it when I reached the 80s, then I passed me at 40, other times at 90.
I change the radiator, change the fuel filter, change the high pump, change the battery and the problem continues to insist.
What I recommend, which I am doing now (4 months ago that I have the car in this situation) is to lift the 2 wheels onwards and make it walk to a scanner. Because the error does when the car is walking, but it will not mark the computer.
At this time the car is scanning me and a failure in the left brake information appears, which may be sending bad information to the car's computer and that is why it does not let me go to more than a certain speed.
What I recommend is that you do the same to see that it marks you. It is undoubtedly an electrical problem. Some sensor is sending bad information, and this may be due to an overheating of the car that some cable inside the engine may have burned.
I tell you that the same thing happened to me, I just had made the oil change and returning from the field with the garbage covered radiator, the car presylted and began to fail. The big problem of this is that it is not known where it is failing until you escape while the car is walking.
I hope you are lucky and hope to fix the two cars because it is a shame.
Any novelty I keep you aware.
a hug