Hi, I'm relatively new to boating just bought an old runabout with a Mercury 500 Thunderbolt, was running beautifully on muffs until hitting the water, have Mercontrol and idle up was on for about 10 minutes pulled down all the way idles ok, noticed when shifting into forward the idle up lever came up about a quarter of the way with it, didn't take much notice just pushed it back again, when shifting further down to accelerate the engine stalls, starts up straight away but keepa doing that when accelerating. Pulled it out came home had a look around and found what looks like a vacuum or vent hose just sitting there, its located close to the water outlet hole and not sure where it shouls connect to and could this have been causing my issue? See photo of similar hose. Had a service with timing ans carbs etc done not long ago. Thanks any help would be appreciated.