I recently had the same problem with our '90 300E - sputtering and stalling. My problem turned out to be a dead alternator. The engine was running the battery down to nothing. The tough part was that there was no warning light, and the alternator even tested good (off the car on a test bench)! I decided to replace it anyway since there weren't too many other possibilities. That did it. It's been fine for 6+ months now.
I hope this helps...