I'm still new to this GM / Saab TiD engine, but yesterday I was feeling changes in engine behaviour (output) under acceleration. Some times I have plenty of acceleration, sometimes I have next to no acceleration :) and it was varying. This morning it was find...
It feels just like a petrol turbocharged donk when the ECU shuts down the boost pressure because it was getting too high...
I'm thinking an intermittent problem with the mass air sensor, a DTi thing on UK Vauxhalls and given the TiD's origins, sounds plausable. Is there anything else it might be? A collapsed hose somewhere? Crud in the air filter?