One suggestion is to check the steering damper (shock) mounted in the steering linkage. Check for previous posts on this subject. I recall someone replacing one recently.
You can check by disconnecting one of the mounting bolts and checking the action of the shock.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T