My car is a 94 honda civic 1.5L. Lately it has been reving up and down but if i leave it idling for 5 min it stops and idles fine. But then when I start driving again then at a light it starts to rev the same way. It has never tried to die from it. But there is no check engine light on neither. I took it to a mechanic he didnt know what it was either. anyone have any ideas? Please help me!!