idiling problem - 99 Sebring

Engine idiles at 800 RPMs then suddenly jumps to 1200 RPMs then falls back to 800 when at a stop sign.

Several mechanics have looked at the car and have not figured it out.

Any ideas?

Just recently developed the same problem with rpm at 750 then surges to 1200. But my 98 seems to be miss firing at 750. Will troubleshoot tomorrow. Have you found anything?