Hi
I have had the same problems on my 1988 300e. I had several mechanics look at this problem, without succes. That experience was a little costly. With the help of readers of this forum I did several checks from their suggestions.In my case the problem was the temperature sensor contacts, I cleaned the contacts and the problem dissappeared right away. My cost was only a couple of dirty towels.

I hope this will help you. Keep us informed.