p0401 Neverending EGR problem

your egr flow sensor is bad

does the idle go low when the egr valve opens? what does the dpfe voltage read when it is open? crazy idea,but have seen it before,check the vacuum connection at the egr valve,another tech had found a small ball bearing stuck in the vacuum line at the egr valve.if you have 12 volts at the egr vacuum regulator,ground the other side when it is connected,and it should pull a vacuum and open the egr valve,thus lowering the idle,if not making it stall.good luck.

tough code sometimes. you need a vaccuum guage. run it at 2500 rpm and open the egr. the vaccuum should drop 4 inches minimum. if you have a scan tool, you need to see the long term trims change as well.

Did any ofth answers help I have a similar problem

try to remove the throttle body and egr valve then clean the carbon buildup from the egr passage