If I am reading your post correctly,you have vacuum at the waste gate.If there is vacuum to the waste gate,It is quite possible that the diaphram that the push rod connects to has a hole in it.If you have pulled the vacuum line off at the diaphram and feel vacuum at idle,then the solenoid is funtioning.No vacuum,then the vacuum pump or solenoid has failed.If you can check the diapghram with a hand held vacuum pump,that would help to trouble shoot the waste gate.
chuck's