Definitely have a good look at all your vacuum lines. Vacuum leaks will throw this code because the PCM as stated, commands the valve open on deceleration while running the diagnostic, and expects to see a loss of vacuum as reported by the MAP sensor. If you are already leaking vacuum somewhere else, opening the EGR won't cause enough of a change and you'll get a P0401.
Vacuum leaks will cause a lot of diagnostic issues on modern automobiles. Been there, done that... the hard way.