2006 Ford Crown Victoria chug at idle

I could be one of a few things. The first thing I can think of would be possible timing problems or your fuel pump may be going bad. Does your check engine light come on? If so you might want to get it checked out. If it is either there should be some sort of message. Another possibility is that it could be a misfire due to numerous things like bad spark plugs, fried out plug coil, bad intake manifold, or clogged valves. The best thing you can do is get a trusted mechanic to check it out. First thing that should be checked is your car's computer, if there is a problem then it should know. If your check engine light is not on then it still should be scanned because sometimes the light will not come on until it is too late. After checking the computer just start eliminating possibilities.