Mot Emmisions Failure

[gazbrown]

Hi guys and girls, my 99 celica vvti 140 failed its MOT today on emmisions, specifically fast idle CO levels. On the first run it was 0.68 % and the second it was 0.77 %. The level as i'm sure you know is supposed to be less than 0.30 %. On the natural idel test read 0.50% which is bang on the limit. It passed the rest of the emisssion tests with ease.

The guy in the garage said it could be the lambda sensor is dirty and to give it a clean with WD40. Does this sound right ?? I don't know much about emissions but there is a lambda reading on the test which is within limits so if the sensor is not working correctly should it not effect this reading ??

If it is the sensor where does it live ??

Thanks in advance :D