Have a 94 mercedes e420, starts and idles until you give it gas then it cuts out, have replaced both fuel pumps and filter, still does it, what could be the problem

Check for a bad fuel filter, it may be clogging up.

gas or diesel..

yes try getting the fuel pump pressure tested by a mechanic. the other thing it can be is the injectors are plugged try running some lucas fuel system cleaner.

could be clogged fuel injectors or fuel filter could be plugged or your fuel pump is weak and needing replaced,what makes fuel pumps go bad in most vehichles is driving with less than a 1/4 tank of gas,it gets the fuel pump hot and works it too hard

I would check the computer for codes first.

I recently had similar symptoms from my Kia Rio, hard to start, bad idle in gear, etc.
Ended up being the idle air control valve, you can try cleaning yours with carb cleaner and see if there's any difference.
A clogged fuel filter can produce the same symptoms too, that might be the easiest thing to start with, then it's just a process of elimination from there.

Fuel pumps are usually located in the gas tank...Hope this helps.

replace the throttle postion sensor also pull catalitic converter and clean out if it's plugged. You can remove the idle adjust screw and reset it but i would have to give you full proceedure to do that so post here for more detailed information.

sounds like mass air flow sensor on the intake system needs changing. check for vacuum leaks, make sure car has normal tune up done

Hard to say, it could be a dirty injector to and bad fuel pressure relay or the vacuume line to the fuel pressure relay. After that you could change the fuel filter, it may be dirty and causeing your pump pressure to drop when on demand. good luck and hope this helps