? 90 tlr thermostat

I have a 2006yr 90tlr. I have noticed that during idle or idle speed in gear that my engine quites once an a while. I also noticed yesterday that i could not get the thermostat to open up while i was flushing the engine. I have been doing some reasearch on thermostats and came across something that lead me to believe i may be having a thermostat sensor problem that is causeing the kill at idle. Do any of you know of a problem like this?

Other than this there is no problems with the engine. I bought it new and have kept up with it. aprox 90 hours of use.

[boats.net]

It would have to be stuck completely shut, test it in a pot of hot water.