the 88-94's use air struts. air bladders on the struts (the bladders replace the springs). the damping is controlled electronically (well, an actuator on top of the strut, connected to a rod that goes inside the strut and controls damping).
Just pumping more air into an air spring or even an air shock dont really do anything other than increase the rate (usually resulting in extention of the air spring or shock.)
air is a miserable material to use as a dampening medium. it compresses way too easily.
I usually dont think of 'firm ride' as high spring rates, but high damping rates. higher spring rates usually result in the vehicle sitting higher (unless you shorten the spring to compensate for the increase in height).
only way I see for an air spring to firm up a suspension is to have the suspension travel limited and the suspension is at the limit, so the spring cant extend any.
My 91 rides exactly the same with just me (about 270 lbs) as it does with me, my wife, my father-law, and my kid in it (total of close to 1000lbs of people), at the same ride height as just me. only difference is, once we all leave the car (take weight out and let the suspension extend again), we have about 5 or 6 inches MORE ride height, until all the doors are closed, then the computer vents the car back down to normal height. There is a LOT more air pressure in the springs with the car loaded down, and it still rides the same. that tells me the air pressure in the springs is only increasing the ability of the strut to hold up more weight. the firmness never changes regardless of how much tonnage is in the car.
