Definately your vacuum lines. Had this same problem, though I got mine fixed professionally. Mine sat for a little under 2 with minimal use. Took it in and the lines got replaced.
2000 2.5L Ford Banger
What I've Done: Pioneer Head Unit, Nexen 31" Tires, Projector Headlights, Manual To Power Locks, Jet Black Paint Job, American Racing Baja Rims, Billet Grille, Herculiner, Rail Caps, Tinted Windows, Explorer Radio Bezel, Wired Bezel For Projectors, Kicker Sub/ Visonik Amp, Black Carpeting, Kicker 6x9 Speakers, High-Flow Air Intake, New Horn, Black Interior. Center Console, many more still in process.