Intermittent high revs at tick over

[Steved55]

Hi - 2016 t6 shuttle, ad blu, stop start dsg. Currently 70k miles. Been driving faultlessly but occasionally when at standstill if I put it into neutral, revs will slowly climb up to 2500. Throttle pedal will not respond. Switching off the ignition stops the engine ok so it's not a runaway and no exhaust smoke. Restarting always results in normal tickover. If I'm brave enough to let it rev on it will eventually slow down to normal.
Any ideas please? No warning lights and my basic obd shows nothing

 

[mmi]

basic obd shows nothing

OBD standard is for emission faults only - so quite possibly is not showing manufacturer specific engine faults?

 

[Steved55]

This problem is slowly getting worse. Frequently now when at standstill if in neutral or park, revs will climb to 2500 - throttle blipping then does nothing. Put the gearbox into drive and the revs drop to 900. And the van drives fine.
Google ai suggests faulty idle air control valve - does this exist on a t6?
Do I need to get a full scan done?
Anyone near Grantham got Carista or similar?
Help!