I'm not entirely sure if a 1992 GS is the same as my 91 LS, but heres what I can offer:
first, get some brake cleaner and sprits some around all the various vaccum lines under the hood, if theres a leak anywhere your engine will freak out for a moment when you sprits the cleaner on it, thus telling you where the leak is. a leak in the vacuum line can cause funny idling and running
secondly, check out the information i gave this guy:
follow the instructions I provided him to clean the CIAV. This is something apparently not many people know about that can cause funny running issues, so even if your car was well maintained this probably hasnt been done on it. My car would idle and sometimes run funny, i adjusted and cleaned the CIAV and now she purrs like a kitten and idles right where shes supposed to
These arent the guaranteed fix, but theyre very easy things to do and can potentially be the issue, and the ciav should be done anyway.