my check engine light is on!!!!

[Da_VTEC_KiD]

well resently i had my engine changed.....since i had my check engine light
and some times when idle or park my car rpm go up and down...for 800 to 1300 and so on.......wut could be my problem

[noodles]

someone else posted about the rev problem........... http://www.topendmotorsports.com/members/showthread.php?t=583

[Da_VTEC_KiD]

well i got my problem fix..... it just i need so more antifreeze in my radiator.....it didn't had enuff.... i guess