I have a 11/94 EF with the I6 motor and after runnning for a while, the engine RPM increases to 1200 revs. My car usually idles at between 700-800 RPM. What is the cause of this and what needs to be changed to repair this issue?

Any help will be appreciated.

most prolly the ISC is sticky
and needsa clean if u look in the document section it wll tell u how to clean it

Various things can cause that.

Idle speed controller
Blocked fuel filter
Throttle position sensor
Fuel regulator
Fuel pump

First thing I would do is the fuel filter. Then after that start looking at the other things I mentioned.

Cheers