What are the most common issues in the Audi 80 engine?

I have noticed some strange sounds and decreased performance in my Audi 80 engine. What are the potential causes and solutions for these issues?

Most likely, the issue is caused by an old or dirty air filter. Try replacing it first and see if there is any improvement in your engine's performance. Additionally, make sure to regularly clean your fuel injector, as it can also affect the engine's performance.