Is the CEL on? Did you scan for error codes? A fuel pressure test gauge can help troubleshoot lack of fuel issues. Unlikely it's fuel filter as fuel starvation from clogged fuel filter usually shows up first under load (acceleration, high speed, climbing hills). Also, maybe get it up on a lift or jackstands to inspect for physical damage from the hard hit to the undercarriage.

Fred

 

This raises a question: nowadays, do people make a distinction between "stalling" and "dying" or not? I had always understood "dying" meant the engine totally shut down and had to be restarted, whereas "stalling" meant it wouldn't accelerate the way you wanted it to, but instead would "almost" die, then finally take off normally. Enlighten me, please.
James

 

Sorry James for not being clear: the car is running rough after starting and is "dying" (engine stops turning) after a few seconds.

Thanks Fred for the pointers - I'll investigate further tonight for errors etc (CEL is not ON). Fuel filter indeed should have more intermittent symptoms/starvation on acceleration, but I have also read a post about some valve inside the filter so I'm not sure which way this valve works and if it could drastically restrict the flow

 

And also the engine does not accelerate/increase RPM - does not really respond well to the gas pedal

 

Update: Fuel pump fuse #6 25A under rear passenger seat is good. Fuel pump relay (the only relay in the fuse panel box next to the battery under rear right passenger seat) is good. Applying voltage (12V or just touching 9V battery) to relay terminals 85 and 86 makes a connection between 30 and 87 of the relay.

After turning the key (just before the engine starts), there is a short delay, pump can be heard for a few seconds, and the pump stops. Is it normal and does it mean the pump is good, or it could still be bad and making some noise? I'm going to read any error codes next...

 

Why haven't you ordered/replaced the $40 fuel filter - Mann or Bosch ONLY - and a few replacement clamps for the MB trickster clamps in there now.

I strongly suggest you get that out of the way as frankly the affordable place to start... yes, the fuel filter has a "pressure" function, and as you say yourself your fuel filter is "way overdue"

 

Considering the mileage on your car, it could be the MAF sensor. You can try cleaning it with MAF cleaner and see if things improve.

 

I would check the fuel pressure at the rail before you do much more. There are some diagnostics in this thread that may help you resolve this issue. Mine was a different problem but related to fuel delivery. For a few bucks you could confirm/rule out fuel pressure as the culprit.

http://www.benzworld.org/forums/w210-e-class/1645448-fuel-pump-extended-crank.html

 

Unplug MAF and try to run the car again.

 

Thanks, will try tomorrow - specially the fuel pressure. I did not know that's so easy to test with the Actron CP7818 or similar. Except that Autozone is not selling them any more (so I've ordered on line for future use) but meanwhile I've got a free loaner of Actron $150 fuel pressure testing kit from Autozone. So no excuses for skipping the fuel pressure testing - not only easy but also the tool is free to use! Should be 60PSI engine turning, and over 36PSI 30 minutes after engine stops turning (after fuel pump stops).

 

Fuel pressure 5PSI, so obviously some problem with the fuel system (check valve is on the top of the engine next to the oil dipstick, visible after removing the engine cover). Got new fuel filter and the pump, but bad news - the 320 Sedan seems to have both of them conveniently on the left in front of the rear wheel, but my Wagon has only filter there (easy access with raising side of the car) and the pump right in the center under the car - very bad access. So next step - towing to a garage with a proper hoist.

 

$3h ($300) of labor to change the fuel filter and fuel pump and the car runs like new . Thanks to all for the comments and advice!

 

Glad that you figured it out and got it fixed. And, thanks for reporting the results back. That helps others that may have similar symptoms.

Fred