Wow, I had a similar problem about a half hour ago.
I was slowing down at a red light, and my car was shaking like crazy. I thought it was the road, because it didn't look too good, but then I came to a full stop and the car kept shaking. I look at my tach, and it's jumping like crazy between 500-700, and even dips below 500 at one point. I swear I thought my car would stall and die (I drive an auto btw). When the light was green I stepped on the gas, and it smoothened out a bit (maybe it was just me or the road, but I think the car was still shaking a bit at 2000 RPMs). It didn't happen again.
Check your Air Filter
, if it's really clogged it could be choking your engine. I checked oil and tranny fluid and they were good. Maybe I should run some fuel injector cleaner...I honestly have no clue though about why this happened.