Im think about buying a 2002 A4 with 1.8T

1st and foremost, timing belt, be sure of when it was last replaced. Check that the temperature guage reads normal, if not, possible thermostat problem. Also check the coolant level and for oily residue in the expansion tank+any signs of milky residue either on the underside of the oil filler cap or the dipstick.. When stationary, blip the throttle, listen for any 'whistling' noises, should indicate any possible turbo problems, faulty boost control and waste gate problems not uncommon with big miles. Does it run smoothly? Ignition coil packs a known problem with Audi/VW petrol's. Finally, when driving, listen for any 'creaking' toward the front end, the front suspension arms are prone to creaking indicating signs of wear. Hope this helps..