If you have a reason to think the lines are bad, replace them. Rubber vac hose costs pennies, or if you prefer, you can buy silicone hose in your choice of color that will last longer than the car, for example from
Hose Techniques
+1 -- Vac hose is cheap! Do a search on IACV or FITV. If inconsistent idle is your only symptom, you need to try and narrow it down better. Could also need all the general tune up stuff. Plugs, Dist. Cap, Rotor, etc.