First to language, if youi have a 1984 280CE as you state, and not a 1974 280CE then you do not have EFI (electronic fuel injection). You do have K-jetronic. If it were a US car it would have had K-jetronic w/lambda and would have had a small amount of electronic control. The european 280CE had plain K-jet with no electronics (the idle air might have been electronically controlled but not fuel.

I would look for a vacuum leak or a defective decel dump valve.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician