Engine is running but no RPMs

Hello,

It sounds like the vehicle might be in limp mode (low power mode).
Typically, the limp mode gets triggered when the vehicle diagnostic system detects a fault in the engine management system, it is there to protect the engine and transmission components from damaging.

https://www.2carpros.com/articles/reduced-power-limp-mode

Did the tachometer stop working the same time when this issue started?
It could be that the ECM is unable to detect the engine speed (RPM) and triggering the low power mode. The RPM will default to zero when there is an issue with the circuit.

Typically, with this type of issues the check engine light gets illuminated. Is your check engine light on? If so, having it scanned to get the codes can help with the diagnostics.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please let me know of any questions.
Thank you.