Failed MOT on emissions

[kaytsd]

I have a 2003 Ibiza 1.4 Sport. The engine light is on and it recently failed the MOT on emissions as follows:
Exhaust emissions carbon monoxide content after 2nd fast idle excessive
The readings are
Fast Idle Test
CO 0.300 Max Limit 0.472 actual value Fail
Second Fast Idle Test
CO 0.300 Max Limit 0.411 actual value Fail

HC and Lambda sensor both passed

Does anybody have any ideas what it could be?

 

[Oj 89]

You said EML is on, have you VAG-COMmed it? May well be the bank 1 Lambda gone intermittant, mine did that and blew my cat up!

 

[kaytsd]

We have VAGCOMd it and have an idea that it's one of the Cat's, apparently there are two on the car. How do we know which Cat it is. The Lambda sensor passed the emissions test.

 

[Slimy]

It could still be the lambda sensor at fault, even if it reads the correct voltage. What has VAGCOM actually come back with?

Cat's are normally numbered from the engine back, the first is near or on the manifold and the second is a bit further back.