[Olds64]

The best way to check for a vacuum leak is to use a Vac-U-Tec machine. It is a protable machine that makes smoke with a little electric heater. You hook it up to a vacuum line and press a button, then it pumps smoke into the engine and it will come out of any leaks.

Of course, this isn't a machine everyone just has lying around. I saw friends at school blow cigarette smoke into the vacuum line but it never seemed to work too well... stupid Ford guys. You can also use starter fluid and spray it around the base of your intake manifold and such. IF your idle changes when you spray the starting fluid onto the engine then you know you have a vacuum leak.

I am not sure about the towel idea.