Erratic tach needle behaior!?
 

So I noticed recently that my tach needle will twitch and bounce back and forth a couple hundred to thousand rpm sometimes when I let off throttle. However when I am appling any throttle pressure or in neutral it does not do this. The only thing I could think of that might be causing this is a bad cam position sensor? but not totally sure sense I haven't messed with it.

I'm wondering if this is a common problem with miata's ?? or if anyone has heard of this happening? Thanks

ignitor is dieng on you prob get a new one and your prob will eb fixed. Since your ignitor is built into your coils this means you will need some new coils.

will a coil pack off a 1.6 work? or only off of 1.8l NA's? Is it common for the coil packs to start f***ing up? I mean the it still accelerates and drives fine aside from my crappy bottom end tune

A 1.6 unit will not work as the shit is totally different.
If you are lucky the tach signal is just going out. Failures arent common but not unheard of, just like any coil given enough time/heat/vibrtion shit will start going down hill. If you have experiened no real preformance loss then i wouldnt worry about it but, and erratic tash signal points towards a ignitor going out 9-10 times. The other 1-10 its the ground under your throttle body try cleaning that off before you go out and buy abunch of shit.