Good morning lads,
Last night I got a completely baffling issue and was wondering if some has any input.
Last week, prior to taking a road trip, I switched out to my summer tyres. While driving cross-country, the car felt sort of unstable and thought that the tyres were crap and that I should probably get new ones.
Last night, on the journey back, the car felt unstable again and somewhat hesitant to accelerate (i.e. it wouldn't accelerate betwen 70 and 80 mph on 8th gear, instead it would require more throttle input to kick-down a gear and would go off). When I pulled over to fill-up, the car suddenly felt perfect - it had all the power in the world and was sticking to the road.
60 miles later, it was back to being hesitant and not willing to accelarate.
When entering the city we have a sort of a inner-city highway, I tried pulling up to overtake from around 40 mph and realized that I had pushed the throttle midway through and nothing was happening. I decided to try to switch to dynamical mode and the throttle and gearbox response were back. Switching dynamic off the car still had power, however steering was weird again, being very difficult to get the steering wheel out of center. When I pulled up to the first stop light, the wheel turned quite noticeably to the right.
After doing some inner-city driving at 20-30 mph, I finally got home, pulled up to the underground parking and almost went through the door - the brake pedal was very hard and the car wouldn't stop from 5 mph. I turned off the car to open my garage door and when I turned it back on brakes were fine again.
Any thoughts? All input on this weirdness will be appreciated, the car is a '15 XF 3.0 SC AWD.

 

Bit late, but the performance and brake issues could be caused by a vacuum leak.
Did you check if all 4 wheels are properly torqued after the wheel switch? Wheels getting loose are definitely good for unstable ride.

Chris