95 Nissan Maxima start issues

A lean mixture is usually caused by a vacuum leak, but can also be caused by a O2 sensor and a few other things such as a bad fuel pressure regulator, fuel pump, temp sensor. A rich mixture can be caused by all the things listed above except the vacuum leak. It is hard for me to tell exactly the cause.

I looked up code 86 which is a nissan code that crosses to the PO173. It doesn't indicate if it is lean or rich. It fuel system malfunction left. That tells me the right bank of the engine is running properly. Now I'm thinking O2 sensor for that bank or a catalytic converter issue.