Motor question

[atlfishguy]

Hey guys been awhile since Ive posted, been out enjoying my new boat, well used actually but new to me. Anyway things have been going good, the only problem I found so far is when I start the motor up it wants to quit when cold, fires right back up just dont want to sit and idle. Now when I get it cranked up and run down the lake and come to a stop it idles perfect, and if I fish say for 15 mins or so, same thing it dont want to sit and idle. Its like once it cools down alittle is when it starts wanting to quit but runs perfect when up on plane hammering down the lake and the stop to idle. I ran a can of seafoam through it when I first got the boat as well as changed all the plugs. What do you guys think is the problem? The motor is a 89 johnson 150 gt just went over the 100 hrs.