I must say you guys have done it again , thanks for all the input.
Pento man even though you were not sure , thats exactly what solved my problem: i removed the air filter and i saw a hole with an allen key head. So i have a feeling that this controls the air/fuel mixture .so i turned this like 4 turns and i immediately saw that my engine stopped vibrating , then i put on the air conditioner and discovered it shivered some more.

turned the allen key tiwce more and it stopped vibrating , infact it the engine became very silent , very quiet. Also i discovered my car was now idling at 10 on the rev counter( well that may translate into more fuel consumption, but am ok with it) at least my car does not behave as if its going to die anymore .

So once again thanks guys u are the best.

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1986 230E (revisions on the way)