2001 Can won't hold idle

My 2001 Honda Accord V6 (EX) with 141,000 miles has problems holding idle. It started out as a problem that would only occur when the engine was started within a couple of minutes of turning off warm engine. Sometimes the check-engine light would come on if the engine stalled. The problem would go away (including the check-engine light) if the car was driven on the freeway at 60+ mph. It has now deteriorated to the point that it is permanently at less than 500 rpm, hot or cold start, with or w/o AC. Freeway driving will not fix it either. The check-engine light frequently comes on, and I have been resetting it by disconnecting the battery.