So I've got a JT Tuning 3" turboback exhaust and 200 cel cat on my 97 V70r. It failed the MOT a couple of days ago on High c0 content, fast idle (around 0.7 - 0.8).

The car has now passed it's mot as I put the original downpipe back on and it went through fine. Shame though, as the car went and sounded well with the JT downpipe on. The car is all running well, no codes and the other two emissions readings were well within limits. I did take the car for a good blast prior to it going on the probe, though ive since learnt that it's better/or a plus to hold the throttle at around 3-4k rpm at standstill for around 4-5 mins prior to probe being inserted!?

Thoughts??