So for my tachometer, it works most of the time but every few days it just stays at 0 for a good 10 minutes into my drive and then will turn on and work 100% even after shutting the car off.

For my Speedo, it works but the needle bounces around within a few mph of the speed I’m going and seems to happen more at higher speeds.

It’s not the biggest issue, but kinda annoying and would like to find a fix if possible

For info, the car was originally an automatic and the owner before me had swapped in a TII Manual Trans.

 

Has the car not been ran in a while previous to you owning it? A few years ago, I had my Speedo cable pop out and I just left it unplugged (since the holding mechanism broke). Years later I finally fixed it and the needle was bouncing as you mentioned, just kept driving it and it fixed itself in a few weeks, guessed something in the speedometer itself was just gummed up from not being used. FYI the car gets driven ~50 miles a year… not a joke.

For the tachometer, it gets triggered by either the leading or trailing coil. Are you sure they are working properly? Worth checking. I’ve made the mistake of not having I think the leading coils plugged in and my car would drive but not pull and hit a wall on heavier throttle/any boost. Turned out I didn’t have the leading coil plugged in. Good to verify they’re working in the first 10 minutes as you described.

 

I bought the car 2 months ago, the engine was rebuilt and I was told it had sat all winter. Since owning it I’ve put almost 2k miles on it so I figure the Speedo would’ve worked itself out by now if that was the issue, it also reads the wrong speed after 70mph and gets slightly worse the faster I go. Around 70 it’s about 3 mph off and around 110 it’s about 6mph off.

For the coils, I’ll have to look into how to test them properly. It’s an NA s5 and I’m only seeing stuff for testing FD 13b but I’m sure I can find info with more digging. The engine runs great all the way through the rpm range which makes me think the coils are probably okay but I’m still new to owning a rotary so I’ll check

 

Speedometer has a tolerance stated in the full service manual. And the accuracy is dependent upon tire diameter, which even varies between brands.