Hello guys

I'll try to brief about my issue but here are the relevant facts:

I'm not a mechanic so if any of you are able to give advice please spell it out in layman's terms

I have an A4 1.8T (it's a 2004 shape but apparently has the 'new' 2005 model engine etc...)

The orange emissions light came on and the performance degraded... it still drove OK... but lacked the punch it used to have. My local mechanic isn't a dealership but he knows a lot about Audis and BMWs etc and has all the diagnostic software etc... He said it was showing as a catalytic converter problem. At the time I couldn't afford to replace the cat but the mechanic said it wouldn't cause any harm to drive it for a few months without changing (don't know if that's relevant).

After a few months I got him to replace it, but after a few days the fault returned. So, he's replaced both sensors but it still reverts to a downgraded performance and the orange dashboard light is permanently on.

He's out of ideas now because the diagnostics still say it's a cat problem.

Do any of you guys have any ideas or experienced anything similar?

Thanks