Lately when I turn on my cruise control, I have noticed that every 30 seconds or so I can watch the tachometer fluctuate 500 rpm's down and then back up again to the normal speed setting. By any chance, might this have to do with bad vaccum lines that I believe are located below the battery tray? If so, can anyone tell me what size hose I need to buy? I would rather not visit the dealer unless absolutely necessary.