Could be towing out, well i reckon its showing all the signs of doing so.

Classically if you drive along with two wheels on the white line and the other on a good grippy surface then if its towing out it will tend to veer towards the side opposite the white line as the wheels with most grip pull it over, in extreme cases this can be a very unpleasant feeling as you cross over white lines whilst lane changing, motorway grooves caused by lorries can be unpleasant too as you traverse them.

By the way, check the rear wheel aligment too, and measure the wheebase both sides in case its the rear end out of kilter, or result of a previous accident even a kerb strike thats causing the problem.

Similarly get an assistant to drive your Fiesta whilst you follow it and look all around the car as the suspension moves, i've done this before and its helped with problems especially over undulations and road bumps, if its crabbing in any way you'll see it even if unaware when driving.

Also jack the car up and spin all the wheels in turn, see and feel for anything out of order.

Oh and tyres can play a part, the new steer axle tyres on my lorry react poorly to cambers, the previous set despite wearing really badly, were perfect steerers.

There, that'll keep you out of shopping hell next weekend :-)

Edited by gordonbennet on 15/09/2014 at 22:02

Steering bounces off with presumably little or no self centreing sounds more like a castor issue.

I'd still drive another car and watch whats happening, can be quite illuminating.

To be honest your mechanic hasn't been diagnosing by elimination, he's been throwing parts at it willy nilly by the sounds of it.

Were any of those major parts actually faulty, did anything improve at all.

I don't think you said if it's got power steering or not, might be relevant

Yes, sorry, it has power steering, alloys and tyres are all standard.

Now, one thing I didn't mention, is that there is possible problem with the left dif, there is a low level clicking noise when breaking under 30Mph.

I Googled this last night, and one person associated this with twitching steering.