tachometer acting strange(with video)

[Jaydsm-]

sometimes it doesnt even move, stays at 0k and some times it just does this(video) >>>>

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its a 1998 Spyder GS with the 4G64 NOT the 420a
Car is fine at idle(or so it sounds) and runs fine EDIT: I was driving and thats why when I accelerate it goes up a bit and when I shift it goes back down

 

[brads]

The tach gets it signal from the PTU. Which creates a pulse based on the coil firing. Misfires would cause the tach to misread. So would a damaged wire.

How long has it been doing it, and have you done any mods recently? Stock ignition?

 

[Jaydsm-]

Since I bought the car its been like that, about 4 months. Starter switch doesnt work so we wired a push button directly to start the car. What do you recommend on doing? Tbh my spark plug wires are a bit cheap(came with the car theyre like 5mm). It could also mean a bad coil since it gets the spark from the coil pack?

 

[brads]

The size or price of the plug wire doesn't really equate to how good they are. It can't hurt to change them, and your plugs with good NGK stuff just as maintenance. But I can't say with certaintly that is the issue. Even when you are full throttle, the car seems to run OK, no misfire?

When you rewired the car to run with a pushbutton, did that just bypass wires at the switch?