DF115 won't idle with cowling on.

Kind of a strange problem, motor idles fine with cover off put the cover on and it slowly dies out. Runs great at speed (with cover) had it out yesterday 25 mile round trip no problems until I brought the engine back to idle, was able to get it in gear before it stalled to get back home. At the dock the port motor would not idle, went down today to check out a few things and found out the motor idles ok with the cover off, tried the cover from the starboard motor thinking maybe some kind of blockage stopping the air but same results. Replaced both iac valves at the beginning of the season along with plugs, fuel filter and water separator. I checked and nothing is being pinched when the cover is put on, any ideas on this would be greatly appreciated. Supposed to do a soldiers on the sound outing this Saturday and don't want to disappoint, dealer can't look at the boat until next week. I will be pulling it tonight to take the side covers off for a better look.

could be an exhaust leak, but i think not with the cover on and running 25 miles, do you need to increase the idle speed? what rpm is she idleing at?