Have the same problem here. I was told to replace the "Idle Speed Actuator" No change then they told me it was the "Cold Start Valve" Still no change. The idle fluctuates from normal to 2000. Have not been able to find any consistencies on when or why. Sometimes if you restart it goes away other times no difference. The dealer told me the only thing left is the main control unit and the cost is around 3K. I am not sure what to do next. Let me know how you make out.

Thanks.

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Dean

90' 300CE
80' 300D
80' 300SD