If I am not mistaken, that pipe in the manifold looks very much as if it is part of some form of. Exhaust Gas Recirculation, EGR as it is known !!??
All part of the emissions crap that they stared to put on some cars.
Any how, hold the bottom fitting with a wrench to stop it from turning & undo the top fitting using another wrench.
You can expect that fitting to be very tight due to heat & corrosion , they often are
