possible fuel leak at the rear of the engine at firewall, also any other fuel line location under the hood. Check the VCV valves, as well as the two breather valves and charcoal canister on the passenger side of the engine.
A Stomp test will give you the fault codes - that is a good starting point.
White 1993 850Ci - 251,187 miles
Black 1993 850Ci - 125,508 miles