99 S80 T6 Emission Service Required and Lambda light on

[gl5678]

last Saturday the Lambda light on our 99 S80T6 (with 137000km ETM replaced 18 months ago) lit up, the display showed "emission service required" and the engine runs really rough, vibrates/surged, and no power, there is also a muffed grinding sound on the right side of the engine; does this sound bad? anybody else has this problem before? should I take it to a dealer or an independent volvo mechanic? any advice will be appreciated .