Could be your Booster is "bad," have vac problems or maybe both.
84-86 Fiero and other cars have a vac filter in engine bay like to plug. OE is Metal Can on firewall.
All have a vac check valve that leaks/plug internally after 20-30 years. 84-86 has different valve then 87+ because 87+ uses bigger vac line.
Booster could have 1 of 2 diaphragms fail causing harder pedal.
Could be you have other brake problems causing hard pedal.
Example: MC w/ iffy QT valve can cause hard pedal.
See my Cave, Brake Service
, Quick Take-up notes
and rest of section.
------------------Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)The Ogre's Fiero Cave
[This message has been edited by theogre (edited 06-25-2020).]