Gratch has covered most things, but wandering steering can be caused by the steering being too tight, resulting in you constantly over correcting. Commonest causes are problem lack of oil in the steering relay or top swivels on the hubs too tight (the opposite is more likely) Does it have Free Wheeling Hubs?
Follow Gratch's advise first though.
Whatever the problem bigger tyres will almost certainly make things worse.
...if you can get the relay out!check that both pinch bolts in the drop arm and top arm attatched to the relay are tight also if you can have someone with you to work the steering wheel and spray some penetrating oil on the splines get the other person to waggle the steering wheel and see if there is movement in the splines of the relay and splines of the arms if there is play and the arms are tightened up properly the splines in the relay and or arms are worn, to be on the safe side i would replace the relay and both arms.
graham
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98 d1 300tdi auto.
:doh: But at least it let me look into the steering rod etc properly, lesson learned! :5bblush5:
I had the same problem recently on tarquin (my S3)
get assistant to sit behind steering wheel.
tell them to grasp wheel.
and commence rocking. the wheel....
start at 1foot then 2feet then 3feet, etc and observe each bit of the steering linkage when it begins to move. tackle each joint in turn from the steering box. over a short period i found upper and lower relay clamps were loose. i could just see an oily squidge when the amplitude was sufficient to move it.
How? i don't know. and one clamp bolt was allowing a ball joint to move a little.
all done, and now i can cruise at speed up to 50mph without fear!