* All the ideas are good but I think ajme is on the best track. If your coolant temperature sensor is broken/stuck at a hot setting, it would cause all the things you're experiencing.
* Whenever I get a customer who would like to fix up an older, higher mileage MB, even one that's running ok, I recommend replacing all the temp-related sensors on the motor. That step alone will get rid of numerous, often inconsistent and intermittant (mysterious) symptoms. And temp sensors are, for the most part, inexpensive.
* Speaking of temp sensors, I believe that $100 will buy all the temp sensors (3 or 4) in your climate control. Think of the hundreds of dollars worth of controllers and relays that use that temp information.

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ASE Master Tech
Quality Enterprises
Mercedes Svc. & Restoration
Sheridan, IN
317.769.3536