that covers the entire engine. On the Forfour it is more of a decorative finish
to hide all the ugly parts of the engine. Very common on todays cars.
The covers vary depending on the Forfour you own but they all just pull off.
The engine cover has 4 plastic clips as seen below...

...and each clip has a rubber insert, seen below.

When you pull the cover off, the rubber inserts will end up attached to the cover or to the engine.

The inserts pop over the corresponding stem protruding from the top of the engine.

To refit the cover, push all the inserts back into the engine cover, line up over the stems and
press down to engage all of the clips. This can be made a bit easier if you put a bit of lubricant
on the tip of each stem and around the orriface of each rubber. (stop sniggering).