Hi James,
Welcome to the site :icon_thumright:
The main things to look out for are a full service history, its not got to be a full Audi history but it helps. The 1.8T will last a long time as long as its had regular oil changes
When we're on the topic of the engine you want to make sure the cambelt and waterpump have been changed. The thermostat is also a common fault as is the temp sender. You should be able to spot any issues once the cars warmed up. If the temp needle doesnt stand straight up after a drive then the thermostat could be goosed, if the temps up and down a lot it could be the sender thats ranted. Both easy enough fixes but I'd be looking at the engine oil carefully and smelling the expansion tank to make sure the engine hasnt been ****** by someone not getting the problems sorted.
Keep an eye out for any smoke under load or idle when you drive it.
Common faults apart from the cooling system can be coil packs and the MAF, these are common but not major issues. If a coil pack is on the way out it'll have a rough idle and might be a bit hesitant when you throttle up. The MAF might cause similar issues too.
Listen out for clunks when driving over bumps etc, antiroll bar bushes tend to go at about 70K miles.
Make sure all the electrics work
Make sure the red LCD in the dash (DIS) works properly so you can make everyone else on here jealous as they tend to fail (not mine though
)
Volume knob on the Audi Concert Stereo can develop a fault (no major biggy though)
Look out for a good late facelift model with the one piece headlights. These have a revised interior and are seen as a bit more desireable.
You should be able to pick up a good one with leather, BOSE, climate etc but it might take a bit of looking.
If anyone claims a car is remapped or has any 'mods' then get them to back them up with invoices etc. A good service history and folder of invoices is a sign of a well looked after car.
I'm sure I've forgotten loads but someone else will come along and fill you in.
Oh and make sure you get a 3 door
Tom