I have a 140 hp Mercruiser I/O motor that has just recently developed
an idling problem. When its initially started and warmed up it idles
just fine. When you throttle it up (say 1500 rpm and higher) for a
period of time and throttle back down to idle, the idle drops down to
around 300 rpm or so and it comes close to stalling or actually stalls.

If you were to shut off the ignitinion and start it up again, it idles

jut fine. This process just seems to repeat itself (throttle up and
down, it tries to stall - shut it off and restart, it works fine etc
etc).

I had one suggestion that it was the Power Valve in the carb sticking.
Does this sound right? If so, what is the easiest way to solve the
problem (I've used spray in carb cleaners, but it doesn't seem to have
done much). Does anyone have any suggestions???? Thanks