P0402 after cleaning the air intake

[Exige255]

Hi all,
A few months after replacing the 4th cylinder glow plug, I had to replace it once more.
I've decided to do it by myself and had to remove the air intake and the air throttle.
The elbow was very clogged, while the valve was pretty clean.
I cleaned up both, and, after mounting them back, the P0402 error popped up.
I've recently cleaned up the MAF sensor and used the Liqui-moly 5168 spray to clean up the air intake on the engine head side but the error is still there.

From the OBD scanner, I can see the MAF sensor value increase while accelerating.
The engine runs smoothly when in idle, but it lacks power and the revolutions don't go over 3000.
If I clear the code, it comes back after a few minutes.

Does somebody have an idea on how to fix it? Or something I should check?

Thank you

 

[KJowner]

I'd guess the EGR is stuck open, the amount of carbon build-up may have been masking the issue.
The EGR system is terrible and best disabled.

 

[Exige255]

Thank you for your suggestion.
I've also thought that cleaning up only a part of the circuit could have caused a difference in pressure