I came to the same troubleshooting conclusion last weekend after an intermittent error became persistent. Ordered a used pressure sensor, and of course the problem went away before the part arrived :rolleyes:

S60 knock from rear suspension
 

Had a knock for a long time which sounded like it came from the suspension, but would disappear, and then come from the other side.
we had it on the ramps and could see the rear anti roll bar had shifted sidewards in the bushes - the rubber stops had come free from the bar. Still supported, but now allows a bit of lateral movement.
Garage top mechanic couldn't see a problem leaving it like that. Doesn't appear to affect handling. MOTs all pass. Doesn't interfere with suspension other than a rattly knock over some potholes. Verdict was to leave it alone.

if the sway bar has sideways float put some jubilee clips on the outside of the bushes after you have centred it up

On my s60 2.0 t I had very erratic acceleration and idling. To explain the symptoms: the car idled fine and suddenly dropped idle wanted to stall and then picked it up to 1000rpm and then back to normal. There was no pattern no exact time between these problems. Acceleration was slow at first and then got better once the turbo kicked in but was not perfect. After checking through MAF, Throttle body, boost sensor, intake air temperature sensor, cleaned turbo recirculation valve and checked for boost leaks... I decided to replace all vacuum hoses for the turbo and others too. Those are very easy to do. During the work I FOUND one of my NON RETURN VALVES (I have 2 of those) were letting the air through both directions. Could not tell just by looking at it but once I blow air through it from both ways it was obvious.
Put it all back together and voila :cool: . Hope it helps