I would have to agree with autozone.. It sounds like the high speed fan is not working correctly. The fact that it does not do it with the a/c leads me to believe that.. The fans stay on at low speed with the a/c on. With it off, the pcm determines when to kick the fan on to hi. Try unplugging cyl head temp sensor to see if the fans kick up to hi speed. See diagrams for locations. You will need a volt meter to diagnose this concern.