My car has an intermitent idle problem. When it warms up the idle will surge from 600 to 1300 rpm, up and down. If I put it in gear the problem stops but when driving the car there seems to be a hesitation when accelerating. The problem may not appear for a week or more then it comes back. When the problem is gone the car drives normal. The engine wiring harness has been replaced. My dealer says he has never heard of this. Can you help me resolve this problem