Engine surges, gasoline fumes, diminished mpg

Hi. I drive an automatic 1986 BMW 325 es with 185000 miles on it. I just had the fuel pressure regulator and spark plugs replaced, and am now experiencing extremely diminished gas mileage, engine surges while in park, excessive white exhaust when the car is idling, strong gasoline fumes in the cabin, and vapor rising from the front of the hood after the car has been turned off though it doesn't seem to be "running hot". I talked with my mechanic, who said there might be residual gasoline in the lines, so I drove it for a couple days. I also filled the tank 3 times in the distance of about 100 miles in those couple days. I'm not a DIY'er--no tools, no space, no time to gain the expertise--however I'm not a millionaire either. The car is going back to the mechanic on Monday. What else could be causing these problems? Thank you for your help.