1994 is pre On Board Diagnostics level 2 (OBD2) later cars would have better diagnostic capabilities but require a scan tool to communicate with the on board computer in your car.
Exhaust odor is probably a sign of unburned fuel that is being burned in the exhaust system by the catalytic converter. The engine's rough running is probably due to a misfire that can be ignition, fuel or mechanical. The catalytic converter is designed to clean up excess emissions (hydrocarbons and carbon monoxides) but if you smell this process it is causing the catalytic converter to be over worked and it will shorten the life of the cat convt if the problem is not addressed soon resulting in a more expensive repair.