Well, the fuel systems / ignition systems on these cars are particularly complex. And there are many variations on them over the years. It could be almost anything or a number of things combined, especially after sitting so long un-driven. Just the old gas in the system could have sludged things up. Old vacuum hoses may be cracked. Electrical connections may be corroded. Sensors may be failed. Filters may be plugged. If you are not familiar with Mercedes, then the best advice I can offer you is find a good mechanic who is. If the car was otherwise maintained well, it need not be expensive to get it running well again.

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