I feel for you... although I can't offer good diagnostic advice on your problem (the universe of possible problems is large when someone as incompetent as your prior mechanic has had free rein), I would suggest that you post your location so that someone from the forum can suggest a competent mechanic in your area.

If you are up for doing some diagnostic work yourself, one place to start is to see if there is one particular cylinder that is somehow not contributing, either because of air in the line or low compression, or valve clearance messed up. One way to do this is to crack (loosen) each hard injector line one at a time with the engine idling, and see if the engine problem DOESN'T change. Cracking a line should deprive that cylinder of fuel, and should make the problem worse, or at least different. If you crack one and nothing happens, then you have narrowed the problem down to something involving that cylinder.

Kurt

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- '79 240D - engine swap complete! Engine broken in! 28-31 mpg! Lovin' the ride!
- '86 190D (W201-126) - 2.5 NA engine, 5 speed, cloth interior, manual climate controls, 33-34 mpg (sold to forum member).