I noticed a rough idle on my '86 300E two weeks ago. It also has a noticable hesitation when taking off from a dead stop. Only happens when the motor is warm. Purr's like a kitten when cold. Now for the worse part, gas mileage has gone in the sewer just as prices hit $2+/gal. Was 20 MPG now its 12MPG.
I'm not a FI expert but my first thought is the temp sensor for the fuel enrichment. Anybody else have any thoughts on where to start? I do have the manuals and a good set of tools.