OK here's a write-up on swapping out coils; right hand drive 928 S4.
1) Disconnect battery; I always do both terminals when working on electrics just to be sure.
2) Cover front wing tops with soft towel. Remove strut brace mounted across the engine bay and air inlet pipes to air filter.
3) The passenger side coil is located very close to the front shock absorber mount on the inner wing; look for the coil lead to find it.
4) Once the coil is located, find the hex-head 10mm bolt at the base of holding bracket. It has a black wire also connected by the nut. Using a 10mm socket, undo this nut being careful not to drop it into the engine bay when loose.
5) The semi-circular bracket holding the coil can now be removed. It has cut-outs along the bracket and one is hooked onto a hook-like bracket fixed to the inner wing; it can difficult to see as the wiring loom covers it. Put your hand under the wiring loom and try to feel it so you can jiggle the bracket off the hook. This can be very fiddly!
6) With bracket removed the coil is now loose from the car.
7) Remove the coil lead and lift the coil up onto the towel on the wing top.
8) Only now can you check for sure you new coil is the right type; compare part code numbers on the bottom of the coils; if they match, great!
9) If your new coil is the right one, remove the black cover on the old coil and the 10mm and 8mm nuts holding the wiring to the coil.
10) Attach the wiring to the correct terminals on the new coil and secure with the 10mm and 8mm nuts.
11) Replace the black plastic cover over the coil.
12) Holding the coil by hand put it back into position and reattach the coil holding bracket to the hook on the inner wing.
13) Copper-grease and carefully replace the 10mm hex-head bolt into the bottom of the coil holding bracket by hand remembering to replace the black wire also. Tighten everything up.
14) Reattach the coil plug lead.
The driver's side is exactly the same process but for a few things.
1) Access is very limited so remove the jumper cover, attachment and wiring so you can get your hand into the coil more easily.
2) The 10mm hexhead bolt is near impossible to access. Only using a long ratchet extension can you reach it and you have to access it by standing in-front of the radiator about a third way along the bumper and then feeding the ratchet extension in under the hose going to the rad on the driver's side. The screw is also at a slight angle so it can take some fiddling about to get the 10mm ratchet head affixed properly. Be VERY careful not to drop the nut into the engine bay as it can be VERY hard to retrieve!
3) Disassembly and reassembly are the same as the passenger side.
4) Copper grease your bolts when replacing the strut brace so they're easier to undo in the future.
5) Reconnect your battery and hopefully she fires up better than before!