Well I don't have a solution for you but will share the problem I am having. It may be related. I just bought my boat as well. Mine is in teh shop now and they have not isolated the problem. They say everything checks out ok. Mine is a 1998 150HP oceanrunner. When cold or not run in a few days, teh moter runs quite well, although tomight I thoght it's idle was somewhat rough. During initial use it will power up on plane and runs smooth and strong continuously. It's never given me a problem while running under high power. Then if I idle around for a fairly long period 5 to 15 minutes or shut the motor down and start it up agian after say 10 minutes, it runs extremely rough, also revs up and then sometimes coughs and dies. It also will not rev up or clean up with added throttle, so in that way similar to yours. If you find a fix please post. I'll do the same.