If your Audi trunk lid doesn't stay open or closes automatically the problem may be the trunk gas struts. They are gas-filled struts that can wear out over time. As they get weak they can be dangerous because the trunk can fall and injure you.
Park your Audi on a level surface and set the parking brakes.
Turn off the ignition and open the trunk.
Secure the trug lid or liftgate in the upright position. Have a friend help by keeping the trunk open. Locate the trunk struts that need to be replaced. It is recommended to change both trunk supports if your car has two of them.
Locate the clip that locks the hood support locks to the ball joint.
Audi A4 trunk strut.
Use a flat screwdriver to pry out the clip that locks the trunk strut in place. Install the new strut in reverse order.
Follow the same procedure for the other end. Install the new hood support in reverse order. Repeat this procedure for the other Audi trunk support.
The good news is that you can change Audi trunk struts yourself. In this guide, you will find instructions on how to change Audi trunk gas struts/support. Applicable to Audi vehicles such as A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT.