I have a 1999 S80 T6 Turbo. I know the earlier models have transmission problems and I've had mine since may and I already worry about it. Usually from a cold start (such as omw to work in the morning) I'll accelerate normally and it'll jut forwards accelerating more for half a second and then back to normal. I hadn't changed how hard im pressing the pedal either so idk what's causing it.

On another note my MPG is at 15.7 and was at 16.9 when I bought it and its only lowered since. I've gotten an oil change already and I have some new spark plugs and a fuel filter I want to put in eventually, I've replaced both the cabin and air filter already too if thats the case.

 

Your car has the Magnetti Maerelli (sp) known for failure throttle housing. Do you know how old or when yours was replaced? They mostly never lasted over 100k miles and would cause all sorts of running problems. Have you used a compatible quality scanner to see if there are Throttle codes?

As far as your transmission - Mine lasted 22k miles from new (2004 xc90) - be nice to yours - it will total the car when it starts slipping.

 

All I know is the timing belt was changed as far as anything engine related. I bought it at a used car place on a whim since I needed a daily driver. It has 146k miles on it atm (the car) the only scanner I have is a Zurich ZR13. I'm assuming the throttle housing has probably never been repaired or replaced.