2004 1.6 A3 failed emissions

[SteveAtty]

My 2004 1.6 Audi A3 has failed it's MOT due to emissions. CO max should be 0.3, but 1.2 was measured and the exhaust is visibly smokey
I'm new to electronic fuel injection, so I could do with a few pointers of what to look for to sort out this problem.
It may or may not be related but, when driving the revs do not drop back down to idle as quickly as they did before, they will now sit at about 1500rpm for a second or two before going back down to idle.

So far I have done a oil and filter change and chucked a can of fuel system cleaner in the tank, the air filter looks pretty clean and does not appear to make much difference to emissions if removed.

Can you suggest what to try next to bring the emissions down?

The car hasn't had a decent long run to get properly hot for a few months, so that might be making the problem worse and unfortunately the MOT has run out now, so I can't give it a hard run now.

[Rob69]

for a start you need to hook it up to a diagnostic tool, scan it and and check fuel trims and oxygen (Lambda) sensor output. It could also be a problem with egr or throttle body, check for induction system air leaks, split breather hoses. Dont just throw parts at it. Is the engine MIL light not lit up on the dash?