Idling jumping

[Andy irwin]

I have  a 2010 a4. when the car is in neutral (for example at red traffic lights) it is shaking and the rev counter is jumping. Sometimes this goes away and others it is really bad. No faults have came up on the computer and I have changed the fuel filter and both diesel purge and injector cleaner have been put through. The diesel purge did help for a few days but then back to square one again

does anyone have any ideas what is going on?

[RoyC]