I just occurred this problem today when I was on the way home. I was driving on the freeway, and I step on pedal to full-throttle, so the power kicked in, but about 3 seconds when is was still kicking in, the power just like "pause" 0.1~0.2 seconds and went back to "kicking-in" mode. so I am wondering if that is transmission problem? or fuel injection?

Doesn't sound like a transmission problem to me. If the car went into the lower gear and was going just fine, then it sounds like fuel was getting cut off, or something relating to a loss of power. My car does this periodically and I have heard that replacing the fuel pump relay is a likely solution. Good luck.

so is there any way that I can test the fuel pump relay is bad? by the way, I haven't change the fuel filter for at least about 50,000 miles, is it possible causing this problem?

Fuel Pump Rely
 

Pry the case off of the circuit board and look for a "cold solder joint" ie one of the terminals on the soldered side has a very small line around it (cracked). Just add flux and reheat with a soldering iron to repair. Brian

ABSOLUTELY!
 

Slai,
I highly sugest you change your oil filter. That would very likely seem to be a possible culprit. Mine hadn't been changed in quite some time, and it resulted in a VERY rough idle that only got worse. Try changing it and seeing what happens.
NEXT, I would check out the relay. GOOD LUCK!

I think Dave meant the fuel filter, not the oil filter. Check both of them, the small inline - which you can blow out, and by all means change the main filter at least once per year as it can really reduce your power slowly when it gets clogged.

Yes Ron, I did! Thanks for catching that. I was really trying to figure out what you were talking about!

Mine did the same thing recently while the wife was driving it. Of course she totally freaked out and drove it immediatly to my independent. I got a call at work from him explaining that my wife was there with the car and that he had driven it approximately 20 miles trying to duplicate the condition (with my wife in the passenger's seat) but it did not duplicate. He explained that there is nothing to worry about unless it repeately does it or is accompanied by other problems (ie rough idle, ck engine light, missing, etc) and explained that although a MB is as close to prefection as one can get in an automobile (He loves his Benzes), they do "glitch" on rare occasions.

Hope this helps