Have you checked fuel pump and or ovp yet?
Is the fuel pump delivering fuel at the proper rate?
Is the fuel filter dirty?
Are the spark plugs, distributor, coil, and other related components all good?
Is the Air Filter clean?
Is the throttle body dirty and gunked up?
These are things I would check or have checked.
I'm not a tech though, thats just what I would look at first.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.