My 1995 C220 has been tripping the engine check light for over a month. The code is 400 EGR Flow. It will reset, but tripped again at 200 miles. I troubleshot the system & found the EGR shutoff valve patially blocked with carbon, i cleaned the valve & did a vacuum check & the valve opens at 25psi & should open at 21, so I replaced it. I reset the light & it tripped again at 30 miles, so have I changed out the EGR valve, the EGR mass sensor & replaced all the vacuum lines. the car runs great but the pesty bright red check engine light returns. The engine has never run bad it's only the persistant Red engine light returns. I spoke with a friend of a friend who works on benzes, he said good luck, you've done everything I would've done. Any help out there?