2005 MCSa with 63k miles on it.
Yesterday was leaving parking lot after about 8 hours of sitting (engine was cold), turned to the street and pressed accelerator and got DSC light EML light and car switched to limp mode. Connected ScanGauge and read out code P1689 (that no meaning miscalculation on 2/3 throttle). Turned off and on and all seems ok. I searched forums and haven't found anything pointing to a failing part. Some had bad BPV, some failed MAP sensor, some chewed up wiring harness. I have vacuum/boost gauge, which was installed specifically because car was dropping boost from time to time during acceleration. Vacuum readout is fine 12-14 and 22 while coasting, so I don't believe there is a vacuum leak, but boost is misbehaving dropping in the middle. Before I connect my GT1 to a car (which I doubt would give me anything other then same error message explanation), can somebody suggest possible routes to look for a problem? I did take off BPV about a year ago and really did not like how plastic gasket looked, but I did adjusted butterfly with no noticeable result. My plan of attack was to replace BPV and since I probably be putting car into service mode, I might as well replace MAP sensor. Was going to also look into replacing intercooler boots.
Any advise would be appreciated.

 

In case anybody interested I did make a trip to a dealer and according to a dealer car needed to be re-programmed according to an existing TSB with similar symptoms described.