Buick high idle

I have a 1998 buick Centrey. When the car is started the idle is about twice a high as normal and when you drive the car you don’t have to push the gas because the car will coast at about 40mph. this is an intermittent problem and does’nt happen all the time, sometimes shutting off the car will reset it for a while but the problem comes back.

Do you have a check engine light? You may have to let it idle at this elevated speed for two minutes to get the light and the associated code. BTW, if it has the 3800 engine, they are prone to having the intake manifold crack that year, and that will cause a high idle. It can also cause coolant to leak into the manifold and then into the combustion chambers so you should get it checked.