2003 Buick Century is idling too fast

My 2003 Buick Century, has 78k miles. For about the last 6 months the car is idling too fast occasionally. (mostly when the car is warm.) Sometimes you can turn it off and on again and it goes back to normal.

It used to mean that the engine control module has gone silly and it had to be replaced. These days it may be possible to reprogram it. Turning the engine off and on and resetting it to normal used to confirm that it was the computer (ecm). However; it’s been a long time since 1985.

The engine in your car is particularly sensitive to vacuum leaks increasing the idle speed. Check for vacuum leaks off of the plenum or from the brake booster hose. Some cars will cause the engine to stall or not run, but this one tends more towards making the idle speed increase.