This is on your '95? It looks like an OBD-II code. OBD-II cars have an EVAP monitor and when a code like that comes up, the gas cap is the FIRST place to look. The system is closed and a bad seal on the cap (like it isnt tightened down all the way) will open the system and the monitor picks up the pressure delta.
Post more info about the code since it's not what I would have expected. Where did the shop plug into your computer (under the hood or inside the car)?
I replaced the gas cap about a month ago. I'm not sure where they plugged in. I can also tell you I get some hissing sound that sounds liek it comes from teh bottom of the filler neck of the tank, even after the car is off, it still does it for a few mins.
Do you have your old gas cap? I've had better luck with OEM caps than aftermarket stuff from the parts store. You could swap it back on and see if the issue abates.
The hissing could also be caused by the purge circuit not working and allowing excess pressure to build in the tank. When you remove the gas cap, does it make a lot of noise?
I agree with JT on the code. That is an OBD II code. Your '95 is OBD I ... unless you did something really crazy, lol. Pull codes via the port next to passenger side strut tower. NOT on the inside of the car.