I hope your freind made it out for the trip with something functioning. There was plenty of chatter about the autolevel systems and airshocks overall when these cars were just 10 years old. Non-serviceable pumps, dying exhaust solenoids, chronic leaks, and of course the poor design premise of using shock mounts as a spring perch. Plenty of issues without even gertting into the poor quality dampening of typical oem airshocks compared to a legitimate performance shock.
Not tryna preach but for better than equal money my decision tree immediately steers to regular shocks and Airlift bladders. So easy to install both, and scads better performance each piece doing its own job. If you just gotta have that compressor at all then several JY options available (I recall '90's M/L and dustbuster minivans real plentiful/popular, but can't imagine many not crushed by now).
Sorry not helping with your diagnosis, but this subject got a "why keep bothering" from our cynical crowd quite a while back.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!