It recently started that my RPM goes up and down between 1500 to 2000 at all times until the temp goes normal. Does anyone experience this and can help me out probably fins out what causing this problem? I know something is wrong since this was not happening before.

 

check for vacum leaks @ the throttle body ( make sure you are using the proper thottlebody gasket)

if you are using some junk blow off valve, (ebay) it might be leaking from the outlet, past the cylinder, and into the vacum hose.

if you have a fast idle thermo valve, it may have come loose. you will need to take off the 2 bolts and metal plate from the backside, and tighten the white screw piece. (you might want to remove it all the way, and put some loc-tite on the threads, then put it back in and tighten it all the way, so it doesnt come loose again. )