1998 Jeep Cherokee exhaust smell when idled

Jeep Cherokee 1998 sport 4.0 6cyl. 168,000 miles, when idle I can smell exhaust it has slight sputter and rough idle. In the past have had codes 700,740,171,133 as of now my engine light is off. 2 days ago I had tune up replaced pick up plugs and wires rotor and cap, oil change, air filter, throttle removed and fully cleaned. This caused my engine light to turn off. Car has been running smoothly until I smelled exhaust while in traffic moments before I noticed a slight sputter. Up until now I have replaced both 02 sensors, had my fuel injection cleaned by Tune Up Master all lines have been checked for leaks there are none PLEASE WHAT CAN IT BE? Thanks for your time. Yesterday I began to use 89 unleaded instead of 87 if that could be of any help I changed my cat converter last week I no longer smell exhaust but, engine light came back on it idles a little I noticed my power steering pump has a slow leak and it appears to be dripping onto my 02 sensor ODB code read 171,740, and 700 need help