Ford should have thought of that
Some 2000-2011 Ford Focus vehicles may exhibit an excessive engine vibration at idle, most noticed when the transmission is engaged in reverse. This condition is caused by debris (stones, ice, snow, etc.) lodged in the rear engine roll restrictor.
Inspect the rear roll resistor for debris. Clean out as needed.
2. Remove the cross member-to-roll restrictor attachment bolt.
3. Install the service shield, P/N 2M5Z-16102-AB.
4. Install the roll restrictor attachment bolt and tighten to 35 ft.-lbs. for 2000-2007 models; or 52 ft.-lbs. for 2008-2011 models.