This any good?
https://www.ebay.co.uk/itm/403742325051?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=8u2oe99jtbe&sssrc=4429486&ssuid=IE07kO4STZy&var=&widget_ver=artemis&media=COPY
Have you had a diagnostic check to see if any fault codes flag up?
How old is the battery? A failing battery can cause all sorts of electrical gremlins.
Speak to Audi customer services. If it was listed at the time of order and you've not been notified otherwise then they should do something. Especially under consumer law.
They will fit, but you'll need wings, bonnet, lights, bumper. And maybe a slight modification to the slam panel. Also if you go from halogen lights to xenon's you'll need additional modules, wiring harnesses ect.
Doing a great job so far. Have a look to see if carpets are wet as Audi's of this era had a computer on the passenger floor called a CCM. If it gets wet it can cause electrical gremlins
I suppose keeping it in efficiency mode for a duration of time would test whether it works by an increase in mpg. Dynamic would only see a quicker throttle response
Get this back to the dealer asap as they should fix this foc within 30 days of purchase. As you say could be the cats, could it be egr or dpf? 🤔
When was gearbox oil last changed?