Your engine uses mechanical Bosch fuel injection similar to that used on Volvo, Peugeot, and VW. It was a great system but was easily damaged by water in the fuel or dirty fuel. Few younger guys know this fuel system well any more. Find a trustworthy independent Mercedes repair shop they will be familiar with this car. Check the basics first. These were a great car,many still on the road with huge mileage. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
Check for ignition spark. Use caution when checking ignition spark firstly it provides very high voltage (about 15,000 to 40,000 volts) but it is low amperage, it can give an unexpected shock but is unlikely to kill anyone, secondly the spark produced can ignite any flammable gas or liquid (for example gasoline or the gaseous vapors of a lead acid battery). Remove the spark plug wire (or ignition coil if the ignition system on your car is coil over plug type), place an old spark plug with the gap between the electrode and shell of the spark plug "widened" to about .060" or .070" of an inch. Firmly ground the spark plug shell to a good engine ground. Hold the spark plug wire or coil with an insulated pliers and get a friend to crank over the engine while you watch for a pulsing bright spark jumping across the spark plug gap. Look on Youtube for a video on "Check for spark" or Check for ignition spark" I am sure someone has posted a good video clip.