I have a 2001 Buick Century. Lately, after driving around long enough for the engine to get hot, the idle speed will sometimes race. The car will want to surge forward even when I'm not giving it any gas, and will roar when I'm in park/neutral.
It can happen while driving, or sometimes it'll act up only after I've stopped the engine completely, grabbed some groceries or whatever, and restarted the engine. Sometimes it'll just fix itself while driving, but other times I have to stop the engine and let it cool down completely. It never acts up when starting cold. No check engine light.
Any advice on what the issue might be, or where I can begin diagnosing the issue?