Thank you very much to jrs2000, Sergio and Deanyel for your suggestions.
I think this car has three coils but I would not know how you check them. The spark plugs are MB items and were renewed around a year or so. At the time the spark plug wires seemed to be in very good condition.
The oil I use is Total Quartz 7000 10w40 (semisynthetic). I change it (along with oil filter) every 3500 to 4000 miles.
I will definitely check the fuel regulator and get back to you.
I very much appreciate your input.
