That is definitely the rubber tube that covers the idle adjust screw.
It has holes in it and a brass collet inside. It should be fitted with the holes nearest the plenum / screw.
I junked mine - But I am concerned by the holes and the brass thing in the tube - looks like it is supposed to do more than just guide a screwdriver..... oh well.. mine fell down the back of the engine never to be seen again....
Cheers
GeeTee 8)