My Alfa 159 2.4 JTDm had a rough idle and after reading thoroughly across forums and cross examining solutions, decided to give it a go to solve the problem :
1. Used Jubilee clips instead of original ones for the intake pipe and connections.
2. Took throttle body off, it was filled with carbon gunk.
3. EGR off
After taking the throttle body off, I used a flat screw driver to clean most carbon out the manifold area. Put hoover hose to suck out the loose gunk. There are tiny passages which was blocked with carbon. Basically not allowing the EGR to perform well.
I would like to remind I've been having issues with idle when engine was warming towards 90 degrees.
I have used good quality brake cleaner and had a injector flush done at the same time.
Now that I have done, the engine sounds more quieter and offers excellent smoothness across the revs. Make sure the throttle body is cleaned thoroughly.
Now I am on the next issue, hopefully I can solve it with your help :
I am getting a tick tick sort of noise around 1500 rpm as you progress through second gear. It soon disappears after 2000 rpm and no sound at all at idle. I can hear it coming from the fan belt area.