Emission Warning

[LouiseR]

After sitting in the garage with a quarter tank of fuel for 3 weeks whilst on holiday shortly after getting back the emission waring light came on. Garage said it was probably just a bit of deposit going through the system and it would go off, sure enough after a week it did. about 4/5 weeks later it was back and stayed on for 10 days. This time garage actually had it in charged me £55 for the privilege of telling me all they could think of was a dirty after market air filter. By this time the light had gone off again.
Changed the air filter whilst I cleaned it just in case. 2 days later yes the light was back.

Also whilst was driving the other day the ECP light came on and went off although it hasn't been on since.

Any advice please before this becomes any more expensive!

It's an Audi TT 3.2 2005

Thanks