I created this list for a friend of mine who bought a TT late last year that may be helpful:
Check the dashpods, coilpacks, window drop, maf sensors.
Get a Warranty!!...no seriously as I'm sure others will point out there are some well documented problems with the TT and they're expensive if they do go wrong....remember it's a performance car so parts aren't cheap and Audi charge about 95 quid an hour to fix things...I have had two Audi's both bought from main dealers for the warranties alone....touch wood my 2000 TTR has been fine but my 2.6 1997 cabriolet had 2k worth of work needed but all done under warranty
The early models were not subject to the coil pack failures
Check service book has been stamped by dates / mileage due
If poss get the Reg # & call a dealer to check that recall has been done & nothing out of the ordinary done e.g accident damage
Turbo, gearbox etc should be lasting 150k + but as suggested earlier get a Warranty
Check all usual things when buying a used car - VIN, reg doc, MOT, HPI etc etc
Get the VIN No and phone Audi Customer services, they should be able to tell you the history.
Spec wise, look out for ones without ESP, they just have a blank button to the left of the hazard warning switch. A few may be without a rear spoiler also. BOSE seems to be a must, and CD changer is desirable. If you can, aim for a fully laden 180, with climate control, DIS, Xenons and bigger alloys. There are a quite a few out there.
The ESP & spoiler was part of the recall although some owners didn't want to spoil the lines & opted not to fit the spoiler.
Audi decided that the airflow-sensors in the following TT's (recall 24H3)
'99: X1000101 to 026901
'00: Y1000001 to 091269
have to be renewed with airflow-sensors ending with D (180) and E (225). Normally guaranteed..