Diag Codes - Bonne 1994, Stalling, any help

I have these diagnostic code read today from 1994 Bonne SE.

P0131 - Oxygen Sensor signal too low

P0134 - Oxygen Sensor circuit problem

P0171 - Fuel Trim sensor lean

Could any one out there help me. Should I change the oxygen sensor first or worry about the fuel system.

My car is stalling at both high and low constant speed expecially when I am in traffic where I can only go at near constant speed. It happens when I am about to get to stop sign after reducing the speed to even level.

Any help from LMP and the rest of the guys and gals!