I experienced something similar with my 94 c280 last autumn when the mornings started to get cold. It only happened when it was cold in the morning, around 15-20 farehnheit. The gas that was in the tank was over a month old, and still on the summer formula. He suggested trying a lower octane gas, so I used 91 instead of the 94 I normally run. When I went to the 91 octane, which by that time was formulated for winter conditions, it instantly cured the problem. The technician said that if this didn't cure the problem, the next likely culprit was the coolant temperature sensor.
Does your starting problem happen at all times, or just when it is a little cooler than usual. I can see you are in California, so cold for you is probably different than cold here in Toronto, Canada. But I would try a lower octane gas first and see what happens.
Jonathan