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

After replacing the throttle actuator, I needed to let the ECU relearn the actuator. After leaving the ignition on for about five minutes, the car has been running and driving perfect.