Hello, 

 

2010 1.6 CR (TDi) has just developed a rough idle when warmed up. It's idling around 600-700rpm. The engine feels like it's about to cut out and almost like it's misfiring. Once the aircon is turned on, the car idles around 900rpm and seems fine. 

 

Any ideas? I have access to VAGCOM, but no idea what I need to look for. 

 

Thanks! 

I think you have an intermittent fault with an oxygen sensor that is causing this. I had it with a petrol engined Corsa some years ago. Turning the air con on eradicates the problem because that automatically increases the revs at tickover. as you know My local independent electrical place found the fault and quoted £133 to sort it.  If you have got a local independent electrical near you give them a call and find out what they charge for a diagnosis. I paid £24  some years ago. The fault always came out of the blue and the tickover was reduced to 500rpm and the car was on the verge of stalling and was " hunting" and it was all very uneven. I found that taking the car on the motorway and  driving it hard at speed always sorted it out.... but it always came back. Good luck, hope this helps!

sounds a bit like an injector to me...

 

does it sound like this?

 

 

Did you have the battery disconnected prior to fault?  The ECU ,ay be trying to re-learn your driving habits. It is recommended to drive for a while at varying revs/gears/speeds, after re-connecting the battery, so as to let the ECU learn the fuelling/idling values, etc.