Hi
Our 2013 1.4 TSI ACT has just failed its MOT on emissions. There are no warning lights and no fault codes.

VW have reached a dead end (after about an hour and £100) and want to start changing the CAT & lambda sensor despite their diagnostics saying they are both fine. £££££

It drives fine and economy is the same as ever but emissions are way out. Idle CO is 1.69, limit 0.3, Fast idle CO is 1.03, limit 0.2, Lambda up and down, in and out of limits mainly out. HC all OK.

My local chap now has it and so far found nothing either, and tested it on his machine with the same results.

It sailed through every other MOT. The only work done since last year was a new cam belt. VW did suggest it may be a tooth out but wouldn't that throw up codes, run rough and or drink fuel?

Any ideas from any teck people?