Volvo V50, quick jerking and doubled consumption.

Hi community, have signed me up extra because I and my mechanic are absolutely helpless. First of all. Volvo V50 Built 11/2006, 2.0D. Now to my problem. If I drive relaxed with my darling (with cruise control and speed doesn’t matter) it starts to jerk at once. It is a minimal jerk like a heart sting in humans. This happens at different times, weather etc. Then we have the problem e.g. at speed 50kmh instead of a consumption of 4 liters. 8 liters is to be read on the on-board computer. Nothing is displayed in the on-board computer, no light. The car was already with the mechanic and he repaired everything possible, this following error was shown. -Instead of 4.5 liters of oil was about 8 liters inside, must probably have been diesel with, oil change was made etc. – air in the fuel line, also fixed since the Volvo sucked it in somewhere. After many euros less I picked it up and it consists imme If anyone can help me, I’m desperate, and I’m getting pretty clumsy at the cash register because of this gas swallower…