95 Pathys were OBD I, so a trip to local auto parts store for code retrieval isn't going to work in this case. You would either need a Kent-Moore checker box...which can be hard to find at even some dealers...or just read the red and green LED's on the ECM. One thing about the OBD I system is that it was a bit crude by todays's standards (although, it was state of the art when it was first introduced), it took a real, hard failure to set a code and the code will remain until it is erased. With that in mind, take any stored self-diagnostic codes with a grain of salt; write them down, erase, and go for a long road trip and recheck to see if it resets. Also, don't be surprised if there are no codes...which will show as a code "55" in self-diagnostic mode...even if the engine does run poorly. A site that fives code retrieval information on the OBD I system is:
www.troublecodes.net/Nissan?
Make sure you check your basics: the condition of your secondary ignition system (plugs, cap, rotor, wires), condition of your filters, check for vacuum leaks, confirm proper fuel pressure, check or replace your oxygen sensor (especially if it has a lot of miles on it), exhaust leaks around the O2 sensor, check for excessive play in the distributor shaft...