So it does or doesn’t have impressive power?

Most likely, worn out inner/outer tie rods or excessively worn ball joints. If it’s been neglected it could easily be both.
Maybe I missed it, but does it pull one way or another? Does that pull change when accelerating or braking?

My 04 S80 rack started to get play in the wheel and it was internal wear in the rack. If it is not the suspension or tie rods, check the rack itself. My car has the ZF variable assist rack which was optional on his car. June

It's possible that the one of the two vvt solenoids holes in between the timing belt and 1st cylinder could be uncut. Because I know some engines can only have the exhaust holes cut to be used for the solenoid and has the intake uncut. I'm not sure if it's due to the year or engine model, but that's...

the engine needs healthy vacuum to run properly.
now it runs with positive pressure , but not well.

In no particular order:

- air bubble trapped in the heat core
- heat core is clogged
- HVAC air distributor malfunctions (common at this age)

I did this job 3 months ago when it was too cold to ignore. The housing came with therm' and new temp sensor, it was no good. The bad new sensor ran the cooling fans and prevented the engine from reaching op' temps around 185, the fan kept the temp at 155F tops. Reinstalled the old original sensor a...

Just so you know, Volvo use a smoothed value for coolant temp. The needle on the odometer may be perfectly vertical at 60c-70c, way before working temp. Meaning a stuck thermostat. But, I have had this happen to me when I replaced the heater core. I had to wait for the car open the thermostat severa...

Dumping? To burp the car you don't need to drain anything. And yes, the coolant value is smoothed. The needle is full vertical well before operating temp and stays there up to 125c engine temp.

When I replaced the thermostat with a full coolant flush it took several valve openings to burp all the air out. I had the front end raised on ramps and used the Lislie Spill Free Funnel. That funnel is great for burping air and comes with adapters to fit nearly any radiator.