Fault Code P0171 Passat 1.8T Help Appreciated

I have the following fault associated with a warning light:
16555/P0171/000369 - Fuel Trim; Bank 1: System Too Lean
Looking it up I found the following info:
Possible Causes:
Mass Air Flow Sensor (G70) defective
Intake System Leak(s)
Possible Solutions:
Check Mass Air Flow Sensor (G70)
Check Fuel Pressure Regulation
Check Fuel Pump
Check Injectors
Check Intake System for Leaks
Check Exhaust System for Leaks
Check Secondary Air System for Leaks
Check Vacuum Pipes for Leaks

The car runs great except occasionally when I stop, say at traffic lights after a reasonable run, the idle fluctuates.
If you have experienced a similar problem, I would appreciate advice on narrowing down the possible cause and how you fixed it. Thanks.

I cannot comment on the fault code, but having previously owned a Seat Leon Cupra for 5 years from new, with the same 1.8T engine in it I can say that the idle does fluctuate slightly (+/- 50 rpm) on those engines even when they are in the best of health, so I wouldn't read too much into that.