Oil pressure 1.8 D: I’m going crazy.

Hello dear colleagues, you have helped me so much with the temperature problems and gave me advice on “with 193,000 KM on vacation”. Thank you very much for this. Now I still have a problem that simply makes me crazy and with which I now finally do not know any more. My Fiesta, which is already sufficiently well known to you, is the favorite car in the world in city traffic. Also if I drive normally over the highway or over the country road. But if I only 5 minutes It is only when the car is idle. It is only a short flickering and in the course of time it gets worse. (Test: Autobahnfahrt und Kupplung entstehen). In the city traffic it calms down relatively quickly: lamp is off. Very important: when I give a little gas, the lamp also goes off. In short: Nic drives 120, idle speed: lamp on. Over idle speed: lamp off. At first I thought that it was on the vacuum pump for the Brem oil change was made in September: original oil from Ford. Enough would have to be in it: in the middle of the top and longest flattening on the track bar. My friendly Ford dealer gave me to understand that it could be the oil pump – which, however, I do not like. Hiesse it to turn my small thick trekker off soon next to other cars. Do you have no idea? Can it be the oil pressure switch? What u And when does it actually show? I still have a can of oil sludge flushing here. However, there are little anzecihens for oil sludge: vebtile drive and oil lids look good. I am grateful for every tip. At the moment I am a little irritated: If I still meant that there is enough oil on it, it seems to be too much oil. Anyway, according to the operating manual. Please don’t consider me naive. But I always give the Fiesta to the workshop for TÜV etc. and actually you should d They can’t just be so stupid and tip too much of the expensive oil into me. (Okay, I paid for it too). So what do you think?