Import nodes "node by node"

Feeds and Feeds tamper are really great moduls :-)
But I have a problem with the feeds module

Ok, what do I have to do.
I would like to import about 5000 nodes from a none Drupal-Site, which are living in a CSV-File (I mean the nodes).
The nodes have several textarea with text and links to other earlier datasets in the CSV-File.
So I uses feeds tamper (PHP plugin) to manipulate the links and rewrite them in a proper way.
For example (just a short explanation):
Dataset 742 has a link to the dataset 365. So what I have to do is to analyse the old link, which has a kind of an ID and looked up in the database, which node-id is now the right one. Then I figured out the URL alias and replaced the old link with the new one.
Of course this only work, if the dataset linked to a prevous imported node. Otherwise it cannot work, and I put a error-message in the new link.
That means, the feeds tamper has to do a lot of work during the import.

So far, so good.
What happend is, that sometimes during the import, I cannot figure out the right node-id for the new link, even if the linked node is older then the node, which is imported now.

I think, the reason could be, that the feeds module is not importing the nodes node by node, but it imports a kind of bundles of nodes at the same time.

Is it possible to tell the feeds-modul during the import, to wait, until one node is imported and then go to the next one ?
That would take longer, but the result would by much better.

Greetings from germany

Berthold