2015 S85D steering suddenly jerky this morning. I pulled out of the garage and the wheel was cogwheeling like a parkinsonian's distal biceps tendon, ie shuddering, giving opposing input, to the point that I had to fight it to turn. Continuing the drive it seemed the power steering had a mind of its own, unexpected input, and overcontrol, ie predictably wanting to steer me into the curb every time I took a sharp turn. Only behaving when on dead center or autopilot. I felt like a GAZ-66 truck driver only the oversized steering wheel was swapped for a go-kart version. Somehow I made it through my 15min commute. Called S.C. 0800hours, tech traveled 3h to me with another Model S in tow, test drove, took my car at 1300hours. At 1600hours another tech IMd me to let me know he will work on the car. Tesla rocks!