The 1.8T engines can be fairly reliable. I put about 50k on a 2000 A4 over the course of several years. Timing belt and water pump replacement are a must if you don’t know the service history or when it was replaced (cover pops off easy for inspection) vacuum lines should be gone through and replaced as they get very brittle and will cause rough running / fuel economy gremlins. Overall, if taken care of , the engines are pretty durable. I didn’t have nearly as many problems as the other Audi owners in the forums I was in though .