Charcoal canister Purge Valve.
It is supposed to click... If it doesn't , it is not working [ which is common]
Sometimes they stick in the open posistion. This creates a hard to diagnose internal vac. leak. Can be diagnosed by un-plugging the electric plug and seeing if vac. is coming from the OUT hose. Should not be. I have had luck with wd-40 squirt in tew vac ports to free them up. Sometimes a few tap get them going again..
PS If you have a vac leak related problem and can't find the leak anywhere , look at this valve......