206 Jock, how would you suggest you troubleshoot a problem that isnt there?
If there are no symptoms its a bit hard to find the defect,intermittant ones are the hardest to troubleshoot.
Why do you think it wouldnt be the FCU?
To me it sounds like the Fuel Nozzle would be a good start or even bleeding the fuel system to begin with.
Also possibility of pilot finger trouble..sometimes these problems disappear with a different pilot.
Engineers learn that the hard way!