how can you tell if you have a vaccume leak ( like leaking runners etc ), how will the car act?

well it depends where the leak is to what u will experience. do u think u are having vaccum leaks? if so, explain ur symptoms

Usually a vacuum leak will cause an abnormally high idle. Check all your vacuum hoses and replace any cracked or brittle ones. If you think you have a leak around the runner or something spray around that area with carb cleaner, if you hear the engine stumble then you have a vacuum leak. Be careful when doing this and do it when you first start the engineand it is not hot so you don't have a fire.