This is a genuine BMW cover lid, part number 11 72 7 511 542. The number stamped on the part is 11727511542; BMW's catalog files it under the short number 7511542. You will find it on our Engine shelf, under Secondary air system.
It fits every E46 body style (316i, 316ti, 318i and 318ti, 2001–2004), with the N40, N42 or N46 engines.
BMW draws it on 4 diagrams, among them Short Engine (11_3171) and Cylinder head attached parts (11_3178). It weighs about 20 g (under 0.1 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.