Persistent P0401 code after cleaning

2011 3rd gen 600,000kms

Cleaned the entire egr system, intake channels, valve, cooler, etc, also replaced intake manifold gasket. Intake was so clogged there was 0 flow in 1&2.

no code before cleaning

now have a P0401 that appears after about 70kms of driving. If i clear it, it comes back after 60-70kms or so. (At least the engine runs smoother and better eco)

Also, not sure if I’m hallucinating this yet but i think i can hear engine knock (pre det pinging) once the check engine light appears. Then it goes away when i clear it. Not sure if the ecu makes any adjustments only once the light is on.

To try:
replace gaskets on pipe between egr valve and intake.
Clean mafs

Any other things to try?