On my van code po404 came up so I replace the egr valve and now that code

A professional scanner is needed to check EGR circuit operation.. Did you get the hoses hooked back up to the right ports? Possible blocked passages, pressure sensor (DPFE) or vacuum control solenoid issue but it must be tested to find out!!

POSS VAC HOS ROUTING OR VAC LEAK. DID YOU REPL GASKET?