Engine pulls false air. Loose hose end found

Hello together I’ve been reading in the forum for quite a while and need your help. For some time now my omi has been running very restless in idle mode and is going out now and then. Everything is normal when it is out of the lower speed range. My first diagnosis (can an unsuspecting non-screw make a diagnosis?) was air filter and spark plugs. Both had about 40tkm on the clock and has been changed today in a free workshop. We could not find the reason because of lack of time. He sprayed the intake bridge with brake cleaner. No result. The noise comes somewhere from the area below the wiper motor. I then looked at home again and found a hose that was hanging loose at this nasty narrow spot under the wiper motor. The S Chlauch runs somewhere on the right side of the engine in the direction of travel. Unfortunately it was too late and too dark to follow the story. Maybe someone has an idea where this hose belongs? The hose is made of rubber and has about 10mm outer diameter.