I have a 2005 Mercruiser 4.3 190 hp in a Bayliner 185. After running for an hour or more the engine will run on after the key is turned off. Sometimes just a few seconds but often for 15 seconds or more? Dealer suggested turning engine off while still in gear but this doesn't seem to help much. Someone else suggested ignition timing may be off but it seems to run well except for getting the engine to stop. The engine has only about 20 hours. Thanks for any advice.