P0401 Code of Bad EGR Valve

1998 Acura CL. The code of P0401 said bad EGR valve. We've replaced the EGR valve, Check engine light back on. Got another EGR valve and replaced the newer one again. Check engine light came back on. Then did some checking and replaced the map sensor and the check engine light came back on after two weeks Checked the code and it's the same code: P0401, bad EGR valve. Getting very frustrated at this point. Please help. It's strange that it was fine and then after two weeks, the light comes back on and it's the same code.