1997 E420 Idle Oscillates Up and Down

[85dzl123]

I have a 1997 W210 E420 that starts and runs fine upon getting in the car for the day. Once driven and placed in park, the idle goes up and down as if you're patting the accelerator in a rhythmic motion. I can shut the car off, then restart, and the idle is back to normal. I did replace the throttle actuator with a rebuilt one thinking that might be the problem. What could the problem be?


Thanks in advance,
Joe