That's it, surely nothing further could go wrong

I started her up this morning after fitting a new power steering pump and things seemed fine..
So I then spend the rest of the afternoon washing & polishing her up for the MOT tomorrow and after a final check on all fluids I started her up.. Thought:huh:the tickover's rising now & not settling like usual, so I check all the vacuum pipes & connections, and it's still rising to 2,000 RPM's

Last thing I did was squeeze the breather pipe from the airbox to the idle stabilizer and the revs dropped back to tickover speed.. I let go of this pipe & the rev's go back up again

Am now reading the Haynes bible and have become confuddled.
Any ideas or help gratefully received.