Corolla Verso D4D goes off idle

Hello together, I have the problem with our Corolla Verso D4D 2.2 (approx. 140 hp) BJ 2007 every now and then the problem that it runs out in a warm state in idle. I had the problem between November and March 4 times last winter. Until last week I had rest. Now the problem occurred again. By the way, it was cooler and damp again last week… At Toyota you could not do anything so far, as there was no error in the memory. The injection nozzles were checked with a measuring device On Monday I have an appointment where you want to do a few tests again. But I’m afraid that you won’t find anything this time either. The Toyota workshop has already signaled to me that you can’t do anything if no mistakes are found. Somehow you don’t seem to take me and my problem very seriously either, because they asked me indirectly if I didn’t strangle the engine… What should I do if nothing is found? The car After the last incident last week I was able to start the engine at the 4th try. Before that the car did not take any gas. Besides last winter it was also the case that the engine had already cranked 10 to 15 seconds in cold (0 degrees) before it started (but was only 2 or 3 times the case). Could it be that condensation water comes into the diesel circuit? Otherwise the car runs well and has no dropouts at all. Have their ideas about what it is based on. Thank you so much.