My 91 Accord is having some tachometer problems. It doesn't seem to affect computer or driving. I believe it is in the head unit itself. It will idle between 0-500rpms. Actual rpms around 800. Driving on the h-way it reads 3600rpms. Actual rpms around 3000.
Where does the tach get it input? Can I swap just the tach from a jy instument cluster?

You can probably swap the tach from a salvage cluster, since I haven't seen a '90s era cluster in a while the tach may just plug into the board once you remove the lens and inside trim pieces.

The tach gets it's signal first from the distributor, then it goes to the ECU, on the older cars it may go directly from the distributor to the cluster.

Take a look inside the dist, do you see any cracks in the sensors or rust in the housing?

I'll give it a look when I get a chance.
Car still drives, shifts, normally so it's not something that is priority.

BTW, Fred, I think I got my idle worked out. Once I gave the TB and intake a good cleaning, things cleared up.