I don't think there is a problem with the engine. Mine runs great! No puttering or anything. I think there is a problem with the communication between the gas pedal and the engine or something. The car feels like it just has no horsepower but the engine runs perfectly! Its very strange.

I have this same problem. No codes come up, no lights are on, and Volvo has know idea what's wrong. I have to literally floor it to get it to excelerate quickly. And even then its not quick. I've had all the O2 sensors replaced and the transmission rebuilt and neither have made a difference.