My MB is running extremely rough when stationary. It sometimes stalls out. My local Non-MB repair facility says that my injectors need adjustment or replacement but that he cannot do it. He recommended taking it to a MB dealer for repair. What's involved with adjusting or replacing the injectors? How long should it take? Approximately how much should it cost to adjust? Replace? More importantly, do you think my non-MB mechanic is right or is there something else I should check first?