1996 Toyota Camry RPM gauge

When I started the car I noticed that the rpm needle gauge was going up and down not like it used to. I pumb the gas pedal hoping it will clear something, but it didn't. So I turned the ignition off and pull the key and I noticed that the engine still running and the rpm is going up and down intermittent. I put the key back on the ignition and start the engine again, it did start but did not here the squeaking sound, you know when you start the engine not knowing it's already running, that sound. Anyhow, the same thing still happening rpm still up and down I tried to shift the gear to different positon but still the same. So I decided to disconnect the negative terminal of the battery so it will shut off. What do you think the cause of it and how to fix it/them? Thank you in advance.