Doesn't like to rev when cold

[MTX450]

Hello there, I'd first off like to introduce myself. My name is Dane, I am from NY, and I have an s13. I'm slowely getting into drifting, and am currently on IFXCC. I just had a quick question for you guys. Thanks in advance!!

I did a little searching and can't find the answer to this one. When the motor is "warmed up" according to the temp gauge, and I rev it, it revs up, and then jumps down to idle really quick. Once I'm driving it around for a while, then it drives like "normal". But everytime, when It's cold, it just revs up and down really quickly. Any ideas? Thanks!

BTW...it's a ka24de