Since the car seems to be otherwise running more-or-less normally, I suspect the the piping to the manifold pressure sensor, or the sensor itself, is bad. Check for tubing and hoses going to the sensor that are loose, broken, cut, plugged, &c. While you're in there, do a visual check for any other parts that may have failed.
This may not be the problem or it may not be the only problem. Just something that should be easy to check.
Edit: And it will give you something to do while waiting for someone that knows more about FI than I do.
