After 21,000 miles, and a year with my 2007 MCSm, I have heard the "cold startup" clatter maybe a dozen times. The weather does not need to be cold for this to happen. In fact, the first time was in the summer, after a car wash, with a thunderstorm approaching.

One morning last week, there was a new, but seemingly related, issue when starting out. The engine lost power four times for 1/2 second each, while gradually accelerating from a stop. This was over within about 2 minutes. There was no noise or vibration, and the car has run normally ever since.

I have noticed one similarity in all of these cases. There has always been a big change in humidity / air pressure between the time of parking the car and letting it cool down, and occurrence of the phenomenon when starting up.

So my question is this: does the computer, controlling fuel delivery, aspiration, ignition timing, valve timing (and whatever else), have sensors that are sensitive to changes in humidity and/or air pressure? Does the computer take time to update its settings on startup?

Could the whole cold-start issue be a result of slow sensor-computer updates to the fuel, air, spark, and valves?