Tachometer Problems

[Exo]

Hi all, I have an isssue with my tachometer that bouncing around and sometime stalls out and does not go anywhere. Nissan told me to replace my pinion speed sensor. I think that is also called the VSS but didnt realize it was the wrong part until the next day, so I replace a perfectly good part. Sucks to waste money. Can someone help me out and let me know if there is sensor that I can replace that will fix my Tach issue? And whats the parts name?

Thanks

[MaximA32]

What kind of car is it?