1997 Volkswagen Sharan Excessive black offensive smoking odour

The vehicle emits very black offensive odour like rotten eggs. It makes it consume a lot of petrol. Coupled with irregular steaming. It goes up & down, then off for me to recranck. Although there is one indicator at the instrument cluster being displayed by the vehicle computer as (In 02-service). Please what do I do to get rid of fault. (2) The smoking stops a little if I unplug the airflow metre wire leading to the air cleaner box. But still consume more.(3) The gear refuses to engage once the engine is running. Except I press the gear knob lever before cranking the engine & engage for it to move.