My Rpm needle drops while driving to zero but the car keeps running

This could be an instrument cluster issue or a wiring issue. Some electrical testing is required to know for sure but you can start by taking the cluster out and checking the connectors at the back of the cluster. You can also find services online that will rebuild the circuit boards on these clusters if that's the issue. If you prefer to use a shop for this, use this link to find a good one near you. https://repairpal.com/repair-shops Alex

Also might be worth checking speed sensor signal.

Since the *tachometer* isn't a critical vehicle operations component - you might wish to take no action as for the repair. It may be beyond reasonable expenditures to do so.