Greetings!
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I'm very surprised that the engine management was able to detect a fault and illuminate a malfunction lamp but not (according to the Ford dealer) log a fault code, that doesn't sound at all right to me. Which malfunction light is coming on? It might almost be worth going back to the dealer who supposedly couldn't find any fault codes and say to them that you've paid them £150 for nothing in effect and been left none the wiser, and how can the vehicle illuminate a malfunction lamp yet register no fault code?
Were all other electrical systems in the vehicle normal when the fault occurred (i.e, you didn't lose any other electrical systems)? The fault you describe could be down to a number of things from an intermittent fault with a sensor to problems with turbo actuation control, EGR valve etc. The trouble is, you need a starting point. As it's happening under acceleration when you need power I'd be thinking possibly an issue with turbo actuation or a related sensor (such as MAP- manifold pressure), or defective accelerator pedal sensors but in reality it could be numerous other things as well.
P.S, if it's a 2014 vehicle shouldn't it still be covered by Ford's 3 year warranty or has it done too many miles, or have Ford changed their warranty policy?