Re: RPM suddenly reading too high
Bad tach, or bad wiring, or bad ground. Bad connection in the wiring would be the area I would advise checking first, especially if it tends to bounce around between correct and incorrect rpm. Sometimes accessing the back of the tach and switching the 4-6-8 switch (for the number of cylinders in the engine) helps as this can get dirty. Switch it back and forth a few times, then put it back to the correct setting. I am not sure if this applies to your exact tach- most have this switch, some dont.
