Brake servo (power) unit problem

["Daegrigg (Don)" <daegrigg@domain.elided>]

Posted this before with no response.  C'mon guys and gals I would appreciate some help here. 

91 164 power/servo unit not working.  I hear a air/hissing sound when brakes are applied.  

History,  fuel pressure regulator went bad.  So bad that fuel came out through the plenum tube/AFM.  (My son cranked too much/too long). 

Changed the FPR and car runs good.  After about 1 hour use, the servo unit problem appears. Car still runs OK but idle speed decreases when brake is applied.  Means vacuum in plenum is lowered?   

I am asking myself if fuel could have gotten into the servo;  if so, would that cause deterioration (a hole in) of the diaphragm?  Would hole in the diaphragm cause lost of vacuum in the plenum even with on-way check valve?

Is this realistic?  The servo has a one-way valve is to allow only fir flow out of the servo to create the vacuum. 

Anyone with experience/ideas/help on this one.  The servo is a royal pain to R/R.  

Thanks, 

Don
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