1991 200 Mercury Outboard Stalls In Idle & In Idle Speed. Please Help!?

Hello all. I have a 1991 200 Mercury Outboard. It stalls in neutral/extremely low idle. Without touching throttle, the boat de-accelerates and chugs and then eventually goes back to its normal speed (still without touching throttle). We were thinking it might be the fuel pump or fuel filter, but we are not positive. Do you think that you could help point us in the right direction?