Hi! When the engine is cold, the idle speed of my 85 380SE is normal. It's roughly around 900 rpm when gear is on "P" and 500 rpm when gear is on "D". When the engine temperature reaches above 80 C, the idle speed suddenly increases to 800 rpm when gear is on "D" and 1600 rpm when gear is on "P". The idle speed is very stable and the engine runs very smooth. I am thinking about replacing the idle speed control unit (part # 002 545 3332). I know the high idle speed can be caused by many area. Where should I start to check in order to identify the problem? I hate to spend the money and the problem is still there. I appreciate your help. Regards, Lin 1985 380SE Austin, TX

Most of the time, the acutator will fail and cause the controller to fail too. I usually test them and them end up replacing both if the idle motor is shorting out.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS