I have the same problem.It is a defective rack/sensor interface.Parts are hard to get due to a quality issue at TRW (the supplier of the rack assy).I have a note from ford stating this.I think they regret giving me a copy of this Ford missive. I called Ford corporate,got a return call from Ford Corp./Florida division.The are trying to get a new,non defective rack assy. I also got a case #.I appears the entire rack/sensor/electric assist assy. must be installed as a unit.
Look on my3cents.com for several other people with the same problem.
This problem can be fixed.I drove a different focus and it steered just fine.
We may have to get other people involved if this cannot be fixed in a timely manner.