200 HPDI tachometer Issue

[florida_1959]

I have a Yamaha 2001 HPDI 200 that I am having a tach issue. The starboard tach is the older RED-YELLOW-GREEN multi-function type with RPM, oil and trim. My problem is that at low RPM the tach is all over the place, from 700-1800 yet there is no speed change of the engine. The tach seems to run fine above 2500 RPM, staying in perfect synch with the port engine. I have checked all the connections and they are tight and clean. I dont have any charging or operational issues. Any ideas? I hate to just go for a new tach since they are over $300.00
Thanks

[boats.net]

If you twin engines might try swapping wires on the two tachs to see if it's a tach problem.