I have a '95 855 turbo wagon, about the same mileage as yours. What you're describing sounds like a leaking hose. Inspect all the clamps and condition of the rubber hose sections from the turbo to the intercooler and then to the throttle body. Don't be alarmed by a little oil present at the hose junctions, a mist or a few drops seems to be normal. Also check the underside of the intercooler for cracks/holes.

About the wastegate rod, I'd strongly suggest not adjusting it. Search the forum for the topic. You'll find a few posts about new connecting rods. There's a possibility it has been misadjusted by a previous owner and it's dumping pressure.

If you can't find any suspect hoses, have your Volvo mechanic check operation of the wastegate control valve (mounted on the side of the airbox) at which time he can check for proper actuator rod setting.

I know I'll get flamed, but if I wanted a car with more than 220hp I'd have bought one. Frankly, overtaxing the tranny's in these cars would seem to be the reason one should seriously consider the "benefits" of more power.

Good luck,
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Erwin in Memphis, '95 855t