My 99 vert has been giving a P0401 EGR restricted flow code, this is making my check engine light to come on. I have replaced the EGR valve and also the solenoid that controls the vaccum. I am still getting the code after replacing these parts and rebooting the system (disconnecting the battery). I can't find any vaccum leaks on any of the lines. Has any have any idea where this problem is?