I'm cautiously going to say that I suspect you have one plug wire going bad. However, the situation would be more noticible with a cold engine rather than a warm one. I would suggest pulling the codes, if any exist. As for the plugs, you may want to look at one or two to get a feeling for the condition of the rest. But really, if the plugs are aging, you can expect power loss, poor mileage, and harder starts, especially when cold. Move the MAF to the very bottom of the list as a dirty MAF generally results in engine knock.

BTW, I have seen engines with severe knocking problems that have broke away portions of the porceloin in the plug at the center electrode, resulting in the condition you are describing. Are you having any problems with engine knock?

On edit:

If your condition is such that the engine is actually trying to die momentarily, I'd have the IAC solenoid on my mind (cleaning).