Engine Stalling: Causes and Solutions

Hello, I was on my way to work when the engine suddenly stopped. It wouldn't start immediately, but after about 1 minute. Then it stopped again after about 2 minutes, and started again after about 1 minute. I heard that it might be relay 109, but where is it? I looked under the steering wheel, and there's no relay with the number 109 there.
Next, ADAC arrived, but it seems there was another "show effect" – the car started working again, and I was able to drive to Hasue. It's strange, or could it be the fuel pump?
"But I think I heard a click when it turned off, which would suggest a relay issue, right?"
It's a 1996 Audi A3 1.8 gasoline-powered car.