3.4 PO401 code
 

I have had this code for a while. It says there is insufficient EGR flow I changed the MAP and the EGR valve. The code was cleared with a scan tool but it came back after a few days. Everything else seems normal.Car runs OK. Any advice would be appreciated. Car is an Impala 2003

Pull the EGR valve back off, start the car. One hole should have exhaust pressure the other should have very strong vacuum. You may need to cover the vac hole to start it. It will be a major vac leak the car should idle very high maybe not idle at all without the hole covered. About half the GM cars with the electric valve, the failed EGR valve takes out the computer.

I don't think the computer is bad as everything else works ok. The scan tool shows all the monitors working fine and no other codes. It has 130000 mile on it and I think th port might be plugged. I am going to pull the throttle body and valve to clean it.