I would have a properly equiped shop check the fuel pressure and chamber differential. Also check for a black tailpipe!

Other things that cause trouble are vaccum leaks, bad spark plugs (I assume you got new ones), bad plug wires (you may have the originals, after all), bad distributor, defective vacuum line to the computer on the left fender, leaking idle control valve hoses (you did get new ones, right?), leaking boot between throttle body and fuel distributor horn, plugged fuel filter (usually give rotten acceleration).

You can check the mixture with a duty cycle meter (remembering that US made ones usually measure "upsidedown" on a Benz). If you have trouble setting the mixture to get 50% duty cycle, look for vacuum leaks and a leaking electro-hydraulic actuator on the back side of the fuel distributor.

Also, you can leak lots of fuel on that car without leaving drips, it evaporates off the bottom panel instead of hitting the ground. I had the pressure line fail, you can replace it with high pressure (75 psi minimum pressure capable hose) and hose clamps, the actual line is expensive and has to be ordered from Germany because no one every uses it, they use fuel line,

If that's a sedan, you should be getting 25-27 mpg, not 14 -- my old 280 SE 4.5 gets 14, but it would spank that 300e!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!