1988 Honda Accord LX high idle

Hey guys I had this problem with my 88 and was wondering if you guys would know what's wrong. When I start the car up, it idles high which is no problem what so ever. However, the idle stays at about 1500 and doesn't drop. When I put it into drive or reverse, it drops to normal idle speed. Do you guys know what's wrong or could it be something to do with a butterfly valve/bad carb. The carb was replaced less than 1,000 miles ago though. Thank you guys so much.

Closing dupe thread.