1996 Mercury Sable very very Important question:(

Hi my name's Justin. I have a 1996 Mercury Sable Ls with a Duratec Engine. I started my car one day and all of a sudden I hear this very slow ticking noise, that goes away when i press the throttle pretty hard. When it's warmed up, it sounds perfectly fine. but not when it's first started, it's kinda like a chug-tick kind of sound. please help. I'm going on a 700 mile trip in a couple days, and was wandering if you think a tune up would help? Thanks a million.