rough engine on MB 280 E
 

Hi Friends would you help me please ! I've got my MB 280 E, 1982 trouble on its engine. The idle is very poor and difficult to adjust RPM less than 1500. Eventhough the engine's temperature does not very hot but it cannot run smoothly.
I have asked some technicians and replaced spark plug and its wiring, He did some injector system cleaned up and adjusting all necessary air intake adjuaster on the injection system but it couldnot help to make the engine run smoothly
Some time when I drive on a lower speed with the AC on the engine seems to stall in difficult to start again
would anybody help me please? thank you