600 diesel idle

hello all



ok can you tell me if this is normal, i have a 600 diesel when i rev it and take my foot off the accelerator, the car seems to shudder a bit before it goes back to idle,



how ever it dose not seen to do this so much if i have the air con on,



also when the car idles the revs seem to go up and down just very very slightly, you can see the revs needle move up and down just very slightly.



is then all normal? as my 45 diesel dose not do this?

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