What are these called ?

[steve1968]

And are they difficult to fit yourself ?

The black rubber flap in front of rear wheels, one of mine is a bit ropey, seems like it has steel in the moulding that has gone rusty .

[D.no]

It's an ADL (Air Deflection Lip) - used to aid aero and manage airflow around the tyre.

[STiG911]

If this is a 997 like mine, this is an utter pain.
The steel brackets are bonded to the rubber, not screwed, and there's a lot more to the lip than you can see here - it extends under the side of the car about another 10 inches and is secured by three bolts. The idea is that you undo the three bolts, and the steel bracket 'unslots' from the wheel arch.
Almost every time, the bracket has degraded to the point where the lip assembly just falls off the car once you've undone the bolts.

When I removed mine to clean the inner arch, I didn't bother replacing the metal clamps as I had no way to fix them to the lip.

[steve1968]

Yes, having now seen the part in an image with the clips showing it looks like the large clip has disintegrated and the bits are pushing the lip out , is this the clip you say you just left out ?

I’m guessing it still fits securely without it ?

Car not usually this ditched by the way !

[STiG911]

Hi!
Yes. It stays on without the bracket, as the larger part underneath is held on by the three bolts I mentioned. The whole piece also kind of dove tails into the small rear arch liner, too.
You could, at a push tap a small screw through into the edge of the arch if you wanted a flush fit, but I didn't bother as it's marginal and didn't fancy risking rust encroaching into the hole, regardless of how much protective stuff I'dve used.

[Spice_Weasel]

I have parts diagram if you'd like it. You can order the bits independently. I sourced mine from Jasmine PorschaLink.