It is almost definitely the ISCV, idle speed control valve, needs cleaning!!
Whilst you are at it though set your CO to 2-2.5% CO, and set your base idle, WITH ALL THE PIPES ON, it can be done just fiddly.
Best cleaner I found is carb cleaner folowwed by a liberal spray with silicone polish on the end valve which is the bit that sticks.
Some stick even when this is nice and clean mine does every so often, but not worth worrying about if only now and then.
The idle CO is most important to correct idle, as lean ones will cause a up/down sensation of the idle, and are NOT NEEDED for the MOT test either.
If running ok it will fly through the MOT on emissions with the std CO of 2-2.5.
tabetha