Has anyone replaced the throttle control sensor? If so what exactly does it do?

 

Do you mean the throttle position sensor? If so I replaced it on my 92GXE because it went bad and flooded the car so bad it wouldnt start.

 

Yes, that is what I meant.
Do you know if it will make the car idle up and down erratically?

 

It will if it is out of calibration. I believe the haynes/chilton repair manuals list the specifications of the TPS when the throttle is fully closed and open. For example my 91 sentra's specs are 0.45-0.53 volts throttle closed (idle) and 3.8-4.1 volts throttle fully openned.