S-10 Idle

I helped my friend put in a new valve cover gasket and ever since then his truck has been idleing very high. After he put it back together we noticed that we couldn't find the vacuum hose that goes on the air intake that opens/closes the butterfly valve that allows or disallows hot air from the exhaust manifold. So my main guess is that it is something with a vacuum leak but i've heard that it might be the fuel injector. I am used to my Nova which is carburated so any help out there would be helpful. thanks.

yeah my best guess would be a vaccum leak. double check and make sure all hoses are connected. what year, size motor is it,and i might be able to help?

its a 1989 with a 4 cylinder. Its my buddies car and im just trying to help him out. When in gear it runs fine, but the second you push in the clutch or put it in nuetral it will start to rev up. thanks.