The tach still works but it's been bouncing and has been reading incorrectly when it doesn't work. Sometimes it doesn't work at all after starting the car, it'll read correctly then just stop working after a few seconds. Does anyone know what can cause this, as far as my general automotive knowledge goes, I know there's a gear on the tach that can go bad as well as one on/in the transmission and if what I searched to be true is that the trailing coils also gives a rpm readout.

 

Here's some reading:
https://www.rx7club.com/2nd-generati...ently-1090891/
https://www.rx7club.com/2nd-generati...etimes-444758/