Dependent on what’s found and general experience of this operation, the choice appears to be :
LPG valve saver or similar Remove manifold at intervals and clean valves Exchange the car for one with a different engine
Recent removal of the crankcase breather/air intake connection may help long term. Time will tell.
Have to say, my GDI with 20k under its belt currently displays a virtually straight line power curve and obeys my every command without cough, quibble or splutter.
Chris
2015 Plus 4 Silverlake Blue (2014 3.7 Roadster Crystal Blue) (2012 4/4 Sport Black)