98 Camry code po401

I have a 98 camry 4 cyl and am continually getting egr code po401.

Ive cleaned out and tested egr ,replaced modulator,and the vac switching valve.replaced several hoses also .
Car runs fine,in fact this code came the day after traveling 700 miles .
..it comes back on fairly quickly after properly resetting computer and 1 or 2 drives .
Any ideas as to what else to look at ?

In addition to what you've checked, it could be one of the following among others:
Open or short in VSV circuit for EGR
EGR valve position sensor open or short circuit
Vacuum or EGR hose disconnected
EGR valve position sensor
Manifold absolute pressure sensor malfunction
ECM

I found the problem..as u said ,it was the map sensor!
-but at least i got several other things cleaned out l, and tested like egr,the modulator did also need replacing ,and the vsv tested fine..

what causes the map to go out..clogged air lines or low pressure maybe?

Sorry, no idea.