Intermittent high idling....had enough, help!!!

Hi guys

My Vespa LX50 idles slightly high intermittently.

When in its stand the rear wheel spins also. I am having trouble locating the screw which helps change the idling however in the manual there are 3 type of idling screws and I am still having trouble finding it!

I have 3 questions

1 - Where is the correct screw?

2- What issues can high idling cause? Clutch wear? Belt wear? Fuel wastage?

3- What could be causing it to idle high intermittently?

Thanks in stressed and fed up anticipation

 

could be your throttle cable sticking maybe?

 

It had crossed my mind. Is there any way of lubricating it?