1993 200 hp evinrude.boat has been running great, went to use it the other day and noticed an irregular tach reading ( showing about 300 when at idle ) yet boat was running properly. if I gave it gas it responded but went back to an extremely low level. I tried shutting and starting the boat a few times and the problem seemed to go away.After riding awhile i decided to trim the outboard up and when i did the tach went down as if there was a short, this happened any time i tried to trim the engine up or down. yet the engine was still running fine. took the throttle apart to look for a exposed wire but found none. Any thoughts on what could be causing this to happen. up to this point i have not had a problem with any electrical component 