I had a similar problem with the Carenado C340 last night on a VATSIM flight from Bern to Lugano, Switzerland. The weather at Bern was -5C with a dew point of -5C, a wall of fog. I was expecting icing and applied the appropriate measures. During run-up the manifold pressure would jump to 28-30 inces and die back down to around 20. There was no way to get enough power for TO. I abanonded the flight and sat on the ground killing and restarting the engines, fooling around with icing settings (prop, surface... on/of) and alternate air to no avail. The problem did not go away until I quit VATSIM and reset the weather to CAVOK. I would expect the model to respond to icing conditions. But this is very strange behavior.... especially for a fuel injected airplane. Need to reproduce off-line. Still, Carenado development take notice, pls.