I have an '89 260e which I always filled with 92 or better premium fuel. I have always had a problem with intermittent shuddering at idle.
For about the past month I have been using 89 octane and find that the problem does not seem to occur nearly as much -- practically not at all now. (Sometimes, I panic and think the engine has stopped because I cannot feel or hear it running.)
I read somewhere about a year ago, either here on in the Mercedes newsgroup, that mid-grade fuel was recommended for the 260/300 but I never used it until recently.
Is it safe to continue doing this?