Hello, I hope I can offer you some assistance.
The first place to start with is to have the fault codes read from the engine management, as you say you had this done previously and no codes came up. The only fault that I've seen on 5 separate Focus/Cmax TDCi 2.0 that gives this symptom and hasn't left a code is a crankshaft position sensor fault. Normally if this sensor fails it should give a code and the engine will cut out, but as I say I've seen a few that haven't left a code but I replaced this sensor and the fault has been cured.
I would perhaps have the engine management checked again for fault codes and also make sure that the software in the engine management is the latest level available as software errors can cause these symptoms.
Let me know if I can assist further or if you have further questions regarding this.