I want to thank everyone for their suggestions. In an effort to complete this subject for someone else that may have the problem I will document a possible solution.
I disucssed the problem with a local service
mananager for Volvo
engines. He was very familiar with the problem and said the cause was the low idle speed adjustment was set too low. The fix was to bring the engine
up to operating temperature, then idle the engine and set the low idle to 800-850 rpm
I will not be able to actually try this until I return to the boat next month, but I do remember that the engine does idle around 600 rpm
which is quite a bit lower than the recommended speed.