If the engine is surging, then you do have a vacuum leak somewhere.

The hoses that connect the AMM to the Turbo and the Turbo to the Pressure Bypass Valve become rotted, especially at the "nipple" where the breather hose that runs actoss the top of the motor to the 3 way nylon fitting (the one that connects to the flame trap)

You REALLY have to check THOROUGHLY and I mean THOROUGHLY ! Mine was rotted but it didn't look like there was a thing wrong with the hose until I pulled it off and squeezed it, poked it, METICULOUSLY - then I found the hole/crack/rotten piece. If that S shaped connection hose is cracked or rotted, you better take a seat if you price a new one from a Volvo Dealer, they are like 420.00 for a brand new one.

I can not stress nough the IMPORTANCE of looking for the vacuum leak source. 99 times out of 100, they are the cause of a B230 Turbo running like dogshit.

Also look out the back when you are "driving" the car and you step on the gas - if you see a horizontal plume of BLACK SMOKE behind you on the road, the motor is running VERY RICH, this is another symptom that points to a vacuum circuit leak "AFTER" the AMM.

You could also have a AMM that croaked, have the engine codes scanned if you look for a vacuum leak and can not find one - BUT LOOK LOOK LOOK for a rotted split cracked leaking vacuum line somewhere in the turbo ciruit.

Another place to check is the hose connections to the "TUBES" - Also check the hose clamps and hose connections at the Turbo Intercooler Inlet and Outlet - You could have a "cracked" Intercooler but, it is kind of doubtful. If you DO have a cracked Intercooler, I will GIVE you one if you pay for the shipping, I have a spare one. DON'T replace the intercooler just for the hell of it, make SURE it is cracked by pressurizing the INTERCOOLER and locating the leak and be 100% sure.

Check the vacuum lines on the passenger side of the top of the throttle body, There are 3 hoses there, check cjeck and recheck the lines.

Another way is to get a smoke machine and locate the vacuum leak - see a local garage - one that has a mechanic who can speak Volvo, even if it is basic Volvo.