Low turbo boost - '86 5KCSQ

[George Simmons <gsimmons@sjm.infi.net>]

The boost on my car maxes out at 0.9 these days vs about 1.4 a few miles
ago.  I've performed the checks listed in the Bentley manual and have
come to suspect either the wastegate or the wastegate frequency valve.
The boost behaves the same whether I disconnect the electrical
connection to the frequency valve or not.  Before I pay my mechanic a
visit, does anyone have any suggestions?

 I'm also interested in the actual operation of the frequency valve; two
vacuum(pressure?) hoses in, a vacuum(pressure?) hose out to the
wastegate, plus a two terminal electrical connection from the engine
control unit.....   Anyone know the theory of operation?

Thanks for any comments.

George Simmons