Just purchased a 04 XC90, 2.5T, FWD, 130K miles. This poor Volvo is a pig in 1st gear until 4000 rpm or so, and then it wants to light the tires up. I thought maybe the wastegate actuator linkage was out of adjustment, but It was adjusted 2 turns out. At that point just to see if it would help I adjusted the linkage out 2 more turns. I also found the vacuum hose that connects to a nipple located at the upper center of the intake manifold was leaking. I replaced all the hoses that are associated with that particular vacuum connection point. And another thing I did was I disconnected all the plumbing associated with the induction system, and inspected all pipe/hose for leaks. All the plumbing was in fair shape.

So now I get ready for some big improvement, WRONG!!! Maybe a 10% improvement. The vacuum hose that I replaced was not the correct type hose, and it was sucking flat under vacuum, as high as 15", and boost pressure was peaking around 10 - 12 psi. So another trip to the autoparts store. Instead of hooking up the vacuum hoses again just to go 2 miles to the autoparts store I just capped the nipple at the intake, and left the 2 remaining hoses disconnected(hose to vacuum valve & turbo intake pipe). Now either those emission vacuum hoses play a big part on how the turbo functions or I'm imagining things. I didn't see the vacuum get much over 12", and the boost pressure was peaking around 7 psi now. This time I would say their was a 35% improvement, and the bicycle like acceleration was upgraded to moped.

Also forgot to mention that before I did any of the above I removed the front muffler, and hollowed out the cat. I ran 2.5" pipe from the cat to the rear muffler. Was thinking maybe the cat was plugged or the muffler was plugged.

So I replace the vacuum hoses, and go for a test drive. The power felt the same as when the hoses were sucked flat. The vacuum was 15" again, and the boost pressure was 12 psi again. One more thing, when the turbo is working hard it sounds more like a leaky air compressor hose instead of the classic whistle. When accelerating I hear the turbo spool whistle for like 1 second. So what in the world is wrong with this XC90??

 

That is a tough one, I had a local shop recommend a turbo rebuild place, and took it to them. after reading up on turbo issues, it wasn't worth my time to personally get into it. I ended taking a pic of the turbo vacuum line diagram, and printed up big enough, made sure I wasn't missing any other connections. (color both ends so you still have your color coding straight.