1989 Dodge Aries high idling and check engine light

Hello, in a way the check engine lamp being on is your saving feature. The computer that controls idle speed through sensor inputs has let you know that the malfunction code is stored in the computer and if you read the computers trouble codes, it will give you the correct sensor failure. Throttle position, idle speed motor, coolant and pressure sensors and more could fail and cause this problem. You must scan the engine controller with a scan tool, write down the codes and then you can determine the failure. The best way is to bring it to a shop and tell them the problem, or get a scan tool, scan it yourself then ask again with specific codes about the problem. Your better off towing it to a shop because the scan tool is not cheap. I hope this helps you to go in the right direction. Any other way is a guessing game.