They have to take the intake off, but not the head. The job should pay 2-3 hours or so to do properly including diagnosis of the failed plugs.

You could have a leaky injector or a timing issue/ I have also seen quite a few fuel leaks from the plastic lines. This will allow air in and can cause weird behavior.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS