I have a brand new 2007 Focus with vibration at idle that wasn't there when I bought the car 6 months ago. The dealer says that "They all vibrate" but I don't buy that. It shakes bad enough at a stoplight that you feel nauseous in about a minute. The problem appears to be that the idle speed is too low at 750 RPM. A 4-cylinder was never meant to run that slow. I shimmed the idle stop up about .015" to get a 950 RPM and it runs smooth. I believe that a sensor is giving the onboard engine computer false data and it is cutting fuel/ignition output, causing the engine to idle too low. I had a similar situation on another vehicle a few years back. I am still trying to educate Ford and the dealership about this problem that they cannot seem to solve with their computerized test equipment; their premise is that if there is no "Check Engine" light then there is no problem...! | 
