I have a 20 year old 4-108 with 1800 hrs in a sailboat application. It has run great for the 1000 hours I have operated it. Recently it bagan an unusual behavior. After start up and a run of parhaps 30 min to an hour it's rpm
can be run up/down as normal and will idle normally at 800 rpm
when trottled to minimum rpm. Just like it has done for years. The last two times I've started the engine
after a few hours sailing time (preceeded by the normal operation mentioned), the engine
wants to idle at 1000 rpm at minimum throttle setting. I've checked to see if the throttle min/max screws are loose - nope. Travel of the throttle cable and throttle lever seem normal - no sticking. Any ideas as to what would cause the change in rpm as described?