Engine run Premacy after short distance creepy.

Actually my Premacy (CP 74kW BJ 2000 /7118 214) is very reliable. The cold start runs without problems, usually also the warm start, but for a few weeks there has been a curious phenomenon: If the vehicle is started cold and driven only a few kilometers, the vehicle has start problems at the next start. (Typical driving profile: back to the beverage market and 15 minutes later.) The engine starts up, but runs extremely unevenly, runs out again in idle, whereby the engine is poorly gas and according to Bordcomp. the fuel consumption is between 70 – 90 l/100km. Let the vehicle stand overnight and the next day can be started without any problems, the engine run is round. Also further stops after longer driving are no problem, at the 3rd, 4th etc. Start everything is ok. Sounds strange? There are many parts that can cause start problems on a vehicle, but it is not a general, but rather a rather temporary or curious starting problem. ee, what could that be?