Its a 15 yr old car, it wont last forever.

However- suggets you change the oil/ spark plugs/ air filter/ oil filter. Give it a run and re test. Use quality filters and oil.

Failing that then yes change the sensors. Does it have a catalyst? If it does and the exhause is old maybe needs a new exhaust.

This story has a happy ending. I asked the garage if they would mind re-testing the emissions on a hot engine, and they agreed straight away. They gave me an appointment and I took the car to them. I asked for ten minutes to drive it around and get the exhaust hot; they agreed to this, and tested the car immediately on my return. This time the numbers were

CO: 0.010 %

HC: 11 ppm

Lambda: 1.000

and of course they issued a pass certificate on the spot.

From this we learn two things – one, old Polos never die; two, if you have a catalyst no longer in the first flush of youth, get the tester’s agreement to doing the emissions check straight after a run where high revs and wide throttle openings have been used for some time.