Irregular idle

[alapimba]

Hello

I have xc70 from 2008, 2.4D awd. 301.000km

The engine runs well but sometimes when i change to idle the engine stalls and the RPM become very irregular with a tendency to fall. If i press the throtle pedal it stabilize.
When cruising i never had any problem. Also it never appeared any message on the computer when this problem occurs.
2 months ago when i bought the car all injectores were tested and 1 was replaced.
In june (280.000km) the timing belt was replaced.

Any ideas about this problem?

[mt850glt]

I hope you've already figured this one out, my '02 had like symptoms which turned out to be the CPS, crankshaft position sensor