My RPM Flucuate when engine gets hot?

It could be a o2 sensor only faulting at a certain temp they're very delicate so slitest change can cause it to run like that try a new set of spark plugs to because my car did that before and we ran the computer on it couldn't find the problem ne where and it was a foweled plug or your coil pack could have went bad its hard to troubleshoot a vehicle without being by it I suggest taking it to someone and having it put on a scanner not a code reader like autozone has but a good computer scanner depends on the garage some might charge twenty bucks to check it but it is very accurate that will tell u if it is the o2 sensor and if ur o2 sensor os bad your check engine light will be on.