I saw a similar issue with mine for the first time about 2 months back (same 1.7CDTI too). It did it for the whole day while idling but has never done it since then...never figured out why but wouldn't worry about it unless it does it for a few more days in a row...
As for your more technical questions...will have to wait for the others to come along lol
As for your more technical questions...will have to wait for the others to come along lol