Remove the air intake from your car following
Air intake type 1
With the front part of the intake removed...
use the biggest drill bit you have a punch a hole through it.
Using a dremel/file/rasp and sand paper, enlarge the hole.
Cut a circle of mesh and glue to the back of the cover.
Rough up the 2 faces that will be glued to create a better bond.
Impact adhesive or PU bonding like Tiger Seal will do the best job.
When the glue has cured, reassemble the inlet and put it back on the car.
Air intake type 2
Alternatively you could remove the cover and replace it with something
that looks a little better. This is an 80mm fan decoration meant for a PC fan.
They can be bought from Ebay, Maplin and other computer stores very cheaply.
Mark and drill the 4 holes and screw the fan cover straight onto the air intake.
If you source slightly longer screws you can space the decoration out to make it
flush with the body of the car. You can use off cuts of rubber tube as a spacer.
If chrome is your 'thing' then that is OK, if you want to colour code it I would suggest
rubbing the fan cover down with fine wet and dry paper before spraying it.
Here is OTV's version straight after being painted.
You will also notice that OTV have used diamond expanded mesh
behind his fan cover to stop any stray squirrels flying in there.
And here is his masterpiece in position.
Air intake type 3
I bought a 120mm fan grill from Ebay, this one is a hex mesh and fitted perfectly.
Bend a right angle into the legs...
and then using pliers, straighten the leg out.
Again, using pliers you can either straighten the loops out or cut them off.
(you will cut them off later anyway as part of the design).
Hold the grill onto the intake and mark were the grill legs touch the intake surround.
Using a small drill or a pointed round file, drill a hole and channel it towards the middle.
The legs will push into the holes and will sit in the channel allowing it to be flush.
Push the grill in place and see if any holes need adjustment.
Push it all the way down and ensure it seats correctly and looks flush.
Locate the four legs that have passed through the intake, cut them level...
and fold them flat into the gulley that runs around the inside of the intake.
Replace the foam rubber gasket into the gulley, you may need to trim it to
sit correctly over the bent over legs. With that in place, push it onto the car.
That's it, job done. Unless chrome isn't your thing, in which case, spray it.