The polo revs and then drops

It keeps doing that for about 5

But doesn't stall

1.2 L manual

Dose anyone know what's up with it

???????????

Thanks people

Clean the throttle body and check the rubber hoses connected to it and the inlet manifold for any splits/cracks

as above you may have an air leak, spray a tiny bit of of brake cleaner or engine starter around the inlet manifold and if your revs go up then you most likely have an air leak