motor fouls out after normal start

[klspiel]

I have twin 2007 suzuki 150hp outboards. The issue I am having is that the motors start easily and idle perfect upon a cold start. within about a minute the one motors starts to idle rough and foul the plug with fuel and then stalls. I can usually start it one or two more times until it warms and then it runs fine the rest of the day. I paid a mechanic to try and figure out what was going and and he was unable to duplicate the situation. He had the motor in a test tank and I have the motor in salt water. I was thinking there is a faulty sensor like an o2 or an engine coolant sensor. Any thoughts?