Unstable idle
 

We just bought a 98 civic hx 1.6 with 135,000 miles for our daughter and now we noticed a unstable idle sometimes.even without the ac on. We took it to the dealer and without no codes they said maybe the idle control valve or the start clutchs in the transmission. They did not want to touch it yet untill maybe a code come up or it gets really worse but she is not that bad but it only does it sometimes I don't know what to think the car rides great and no hesitation at all any help would be appreciated thanks