Give this vehicle a full tune-up
1. New spark plugs
2. New Air Cleaner
3. Clean the throttle body
4. Clean the fuel injectors
5. Engine oil flush
Check the throttle positioning sensor and make sure it is within specs.
Check the mass airflow sensor.
Check ECU trouble codes for any emission related trouble codes such as bad egr valves, engine temperature sensor.
Rich exhaust odor can be caused by problems in fuel to air mixture ratio or the ignition timing is retarded or a few degrees late.