generally speaking, the solenoid (and therefore the BstC) is used to raise the boost from its 'base' pressure to about 1.5 x the base pressure.
so if the solenoid or BstC fail, the boost should drop to the base pressure which is usually 13 psi on these cars, or higher.
If the boost is dropping below the base pressure. then it may be something else.
So, if you can see how far the boost drops, that will help diagnose. Also, be sure that you are not leaning out.
Do you have a scanmaster or other scantool/logging method?
Bob