Make sure there is no holes in your exhaust, if there is even a little hole it will throw lambda sensor off. I had a same problem with my car and it was a little hole that was not even spoted at mot.

Best regards

Jarek D.

the lambda is measuring too much air - seal the exhaust. you can buy cat cleaner thats goes in your fuel tank and works for me 9/10 times - also they recommend changing your cat and lambda sensor every 10 years, a fuel filter and spark plugs have been known to cause poor emissions as well- changing them is also a cheap way for better emissions

nah- lambda sensor is another word for oxygen sensor, if it's higher than 1.030 then it measuring high oxygen (running lean) if the measurement is below 0.970 then the engine is running to rich - then your engine management decides to control the amount of fuel going in to compensate- but the emissions machine has its own lambda sensor that can give false reading because of a leaky exhaust - and water in the exhaust is also a killer people driving around town not really letting the engine warm up - the car proberly needs a fuel treatment and a good trashing down the motorway -

anyway off to work to mot some cars myself :)

Start with the simple things.With the bonnet up stand by the engine while an assistant blocks the tail pipe with a rag. If you can hear hissing, there's a leak! I have to say, it doesn't sound like that cat is doing much catalysing...

That failed for an entirely different reason...