I have a 2005 Audi A4 1.8T Cabriolet and I'm having some trouble.

When I drive my car, it runs great but anytime I am idle, my car shakes. I took it to midas and they couldn't fix it but they did determine it was a vacuum leak and they showed me exactly were the leak was. When you pop the hood you can see the hose that has the leak as well as hear it. Its a small black hose that is connected to the engine. When I turn my car on, the check engine light comes on and the drop top light flashes, but then goes off. I'm scared to drop the top. I just wanted to know if anyone knew what the hose in question was and about how much it costs to get it repaired. Thank you.

 

You need to post a picture of it. All the vacuum lines connect to the engine and there are a lot of them.