MAF pipe

[shnazzle]

I don't think it works quite that way but happy to be corrected.
If the MAF is put in a different place or at a different height, it may be reading a higher or lower mass than is actually entering the engine.
Let's say it reads more and you're in closed loop.
ECU adds more fuel.
But there's not enough oxygen to reach the 14.7 AFR it wants.
So it pulls fueling via the fuel trims. Or, worse, it adjusts timing a bit to compensate for the slower burn of the richer mixture. Or both!

It doesn't have a mechanism to adjust the MAF readings as it has nothing to compare it to. So instead it messes with your fueling/timing which may spill into your open loop.

I noticed this happening when I put my Hurricane intake on, so I adjusted the airflow on the emanage and fuel trims are nice and steady and around 0 again.

So the moral of the story is, make sure the MAF is in the correct place in the tube, there are no big bends before the MAF, and if there are slight changes, modify the MAF readings via piggyback/standalone  accordingly.