Head gasket...exact description anyway! Leaks down into the cylinder and causes the rough running on start up, then clears up as it gets warm. Take out your plugs and if they are sooty white, thats the anti-freeze. Fix it now or its only going to get worse and cause more problems. I would smell the exhaust on start up and you should smell the antifreeze. Get your car in and get a rad pressure test to confirm the leak.
