emissions control warning light

[johnny1chance]

Firstly as a new member I'd like to say Hi everyone!

A bit of advice please lads,

I have a 2010 S3 (from new) and 4 months ago at the last service I had the timing belt and water pump done, the day after picking her back up the emissions control light came on and back in she went, apparently it was a breather pipe. 10 days later it happened again, I got her back (no charge thankfully, but no real explanation as to the cause either). all was well until this morning, light on again and booked in for next thursday.

1, how common a fault is this and 2, can you cause more harm by driving with the warning light on, the car drives well with no lumping or pinking but on cold start on tuesday night it did run rough, I turned it off and on restart all seemed fine (put down to cold gremlins).

Cheers in advance

Johnny.