Why does my Audi A6 have poor fuel efficiency?

I recently purchased a used Audi A6 and noticed that it seems to have poor fuel efficiency. What could be causing this issue and how can I improve it?

Poor fuel efficiency in a used car could be due to a variety of factors, such as outdated spark plugs, clogged air filters, or a malfunctioning oxygen sensor. However, in an Audi A6, the most common culprit is often a dirty or faulty fuel injector. This can cause the engine to use more fuel than necessary, leading to poor fuel efficiency.