Im having an acceleration problem with a 1999 e320. I will be driving along no problems, then randomly the accelerator (gas pedal) no longer responds. I have to pull over, turn the car off and let it sit for a few minutes before the accelerator will respond like normal. Sometimes the engine will also die but not every time. Im thinking fuel filter maybe? I get a P0400 code, but I cant imagine the EGR causing this issue. Im completely stuck, thoughts?

 

It is the electronic accelerator transmitter. I'm not sure if that is the correct name but I had the same issue. Take it to a Mercedes Tech and have it replaced ASAP. It could get you killed otherwise! I think it was about $250 dollars or so.
Fairly easy fix.

 

Would you happen to be referring to the throttle position sensor?

 

Had the same issue with my sons 98 E430. If you drove it like an old man (who owned previously) it drove just fine. When you floored it down to the kick down switch it would go into limp mode and set a TPS code. However if you didn't go into the kick down switch it was fine. I replaced the TPS sensor (under the hood by he master cylinder) and the car now runs great. From me research and reading these sensors are notorious for failing. I ordered mine from https://www.fcpeuro.com I think I paid $115 including shipping. Took 5 minutes to replace, very easy!

 

The only code I am getting is P0400 which is for the EGR valve. Its been really tough trying to get this diagnosed without any codes being thrown.

 

That may be the correct name. The car is drive by wire, this is what communicates the pedal position to where ever. I had the exact same thing happening and that solved the problem. The thrown code could be separate and apart or it could be related. I suggest you take it to the dealer or a good independent Benz specialist. I'm 99.9% positive that is the cause of your issue.