1997 altima P0400 & P0325 code

[eddiestar47]

I recently did an intake manifold gasket repair for a P0304 (cylinder 4 misfire). I put it all back together and now I am getting a P0400 (insufficient egr flow) and a P0325 (Knock Sensor). I tried cleaning the egr because I read in a forum that a knock sensor code usually comes with another code, so they said to focus on the EGR. I removed the egr and applied vacuum it holds. I did the checks on the BPT and it as well holds vacuum. i even checked the solenoid valve and it is also working properly. I am stumped and I need some suggestions from someone who did the job and got the same codes or someone who knows why the codes appeared. Thanks in advance.

Ed