I'm having the same problem too on my M103 300CE. I have replaced the following:

1. Fuel Filter
2. Spark Plugs
3. Distributor Cap
4. Rotor
5. Ignition Coil
6. Ignition Cables

Its not an irritating problem but whenever I start her up after a few hours sitting, it'll do what you guys have described - idle rough for 3-4 secs.

I want a healthy start. Any solutions or tips? I've gone to mechanics with differing views. Some even suggested replacing parts I have already done. Oh well...