2001 Buick Lesabre P0400

2001 Buick Lesabre 65k, 3.8 Series II. P0400 code appears about once a week. From what I have read, this could be an issue with carbon build up in one of the EGR ports. I removed the EGR from the intake manifold and sprayed some throttle body cleaner into the ports even though the appeared to be clean. I cannot see into the throttle body to look for blockage because the is a screen over air inlet side. I didn’t record all of the freeze frame data other than it was in Open Loop, Coolant temp was 174 degrees Fahrenheit and key on engine off. It is my dads car and he reported last time he noticed the light after adding fuel. I commanded the ERR to 100% at idle and car still ran but rough. Also when EGR was off the vehicle I commanded it open 100% again and the valve did open all the way up as it should. I head that the means there is a clogged port. Is there anyone out there that can shine some light on this on what to do next?