2008 A8L
 

My 2008 A8L is missing, the check engine light is on & somedays the EPC code will also come on. The diagnostic test is showing the code P0305, the 5th cylinder error. We have replaced all spark plugs, all coil packs, the fuel filter & air filter.
I found a post that said it could be the ignition control module & explained how to test it. It said the module was located on the firewall by the windshield fluid container. I have searched & cannot locate it. If anyone can help it would be appreciated!!!

Your car is a d3, this post should be on that forum.
That being said you car has FSI and is prone to carbon buildup, have you ever done a carbon clean?
It could also be a faulty injector causing your misfire.

Also, there is no module on a 2008 audi.

You need some diagnostic testing done instead of playing parts darts.
-Richard