when my car (5th gen) is on, and in neutral - not moving, say when i come to a stop at a light or something. my car's rpm revs a little from 1000-1500 or somewhere in between by itself and my foot is off the accel. im thinking theres a problem with my pistons? does anyone know?

 

check the iacv, make sure there are no air bubbles in your coolant, and make you have no vacuum leaks, also it might also be your fitv

 

I'm having the same problem when I turn on my car it idles at about 3000rpm and when i gets hot it goes down to 1400-1500rpm. now can you please tell me that those abbreviations mean

 

iacv-idle air control valve
fitv-fast idle thermo valve