Sorry, I wasn't very clear.

Using the guide you linked I swapped over the throttle body, MAF and used a C320 airbox to upgrade to the 74mm TB and 3'' MAF.

Initially I didnt swap the MAF sensor as they have the same part number on them. The MAF is 100% the 3'' version as that additional second layering it doesnt have.

I then swapped the MAF sensor for the original one that was in the 2.5'' MAF.

It didnt make any difference unfortunately.

Yesterday I took a very long look at the system to see what could be wrong. Everything is connected and there are no breaks/rips in any lines. All conectors look sound and nothing is damaged from what I can see.

However I did notice that when the engine cover is pressed onto the 4 catches, the MAF does not sit snuggly inside the engine cover like it should do. It seems to sit with a 2-3cm gap towards the cabin.

I tried and tried to make it line up but was not able too. I got as close as I could get and took it for a drive, found that the car has a flat spot at around 3.5K RPM and when checking after, the gap had increased.

HOWEVER

Today I reversed the process of fitting, instead of attaching the MAF then the engine cover, instead the engine cover to the MAF and then to the throttle body. The cover is sitting tightly on the MAF and on the engine.

Took it for a short drive, got her nice and warmed up, it hunted once slightly.

I'll take it for a proper drive tomorrow if I can find time and report on how it goes. What confuses me is that the throttle position rises, as if its ECU controlled increase, faulty signel from the pedal or a faulty sensor.