1994 Honda Civic Weird Engine Revving

1994 Honda Civic Manual

Once the car gets warmed up the idle is more like an unnecessary revving of the engine. Say you are sitting at a stop light with just a foot on the brakes, the engine sounds like you are revving it (with your foot on and off the gas) even though you aren't doing anything. Please let me know if you have any idea what this could be and how it could be corrected. Thanks!