407 2007 petrol engine flooding?

Yesterday the car was really struggling to idle and even more so giving any throttle. Eventually it stalled and would not start. I called breakdown service and when they arrived several hours later, she started like new and even drove better than ever (no latency between peddle and acceleration). Stumped we shrugged it off but today it has happened again and there is a strong smell of burning fuel. This leads me to believe the engine is flooding whilst driving? Anyone know anything to help shed some light?

 

Had it in the garage twice now, its had new coils, new plugs, new lamda sensor it was serviced 2 weeks ago. The garage have said if its still doing it "it must be something electrical" but they don't do electrical faults.