I had a similar situation with my polo ages ago, when i finally got an answer from the garage it was the EGR valve, no issue with anything else the car was driving fine but the EGR valve was faulty (someone at some point had fitted a cheaper aftermarket part and fitted it badly)
But good luck getting yours fixed,
I dumped mine as after that i had a faulty airbag sensor and problems with the dashboard then the AC gave up and that was the end of that car for me...