Steering wheel wobble
 

Is this likely to just be a wheel/tyre balance issue? At low speed on straight roads there's a noticeable oscillation from the steering wheel - if I let go of it actually moves (rotates). Car drives straight, handling isn't affected, and it clears up with speed. There's no slack in the system, car responds as well as it should to steering input.

I'm running standard Volvo steel wheels (14" or 15" I guess, can't remember) and tall profile tyres. '93 Estate 2l petrol.

Firstly check all your wheel nuts are tight/torqued up, check tyre pressures, check track rod ball joints, wheel balancing and a tracking check next.

Probably a buckled wheel, swap the wheels front to back and see if it changes. Also being steel wheels check for corrosion as a few people have found when they get new tyres fitted the wheel is rotten inside.

Most likely a distorted or damaged tyre , jack it up and inspect whilst rotating the wheel . you should see something out of true ..

Wheel nuts important. Decades ago my dad reported steering wheel wobble on his Austin A40. We found loose wheel nuts on the FNS. Once tightened, no more wobble.
I once had wheel wobble on one of my Triumph Heralds. It started after fitting the spare wheel because of a puncture. Removed wheel and and had it checked by a tyre fitter. Wheel was buckled.
Once had a wobble and pull to one side after fitting new tyres on the front. Tyres were not directional so changed the wheels side to side. Wobble still there but pull was to the other side. Complained to tyre supplier/fitter who checked both tyres and replaced the alleged offending tyre. Problem solved.
Once whilst hauling our caravan down the A1 with my Morris Marina a thumping and vibration suddenly developed. Investigation found that the RNS tyre had developed a “blister” as the tread rubber had separated from the carcass.

In addition to the useful suggestions above, check your spaceship bushes (lower control arm to tie rod) as worn ones can cause this problem.

How is it under braking?

My wheel bearings were worn and the steering wheel rocked gently at 30mph, but near came out of my hand when braking hard at 70mph. It wasn't detectable by normal methods with the wheel off the ground.

940 bearings are not tapered and not adjustable, they seem to need changed around 150k miles.

I had the same issue with my XC60 when I first got it, turns out someone had fitted a really cheap crap tyre to it, which caused the wobble. it got worse the quicker I went. New tyre problem solved.

Vibration through the steering of my 1997 S90 turned out to be the lower wishbones, and specifically the rear bushes.

Jack

Absolutely fine under braking - straight and true, as I found out today in an emergency stop for a buzzard of all things. The ancient ABS on these things is entertaining to say the least!

Will get under it over the weekend and have a poke around. Got a small coolant leak to track down too.