Sorry, must have had an identical response for the same type of car.
Look for vacuum leaks from any hoses on the motor. A vacuum leak will cause this issue.
The throttle body can be dirty not allowing the plate to totally close as well. Clean it with some carburetor cleaner on a rag. Make sure all the carbon is gone.
Lastly, there is an idle air control valve that controls engine speed. If this was an issue it would turn on the check engine light and set a code.
Saturday, March 17th, 2018 AT 4:00 PM