It happens sometimes when at idle only. The RPMs start going really low and I can feel the car starting to shake a little (like just before it stalls) but it never stalls... it just shakes for awhile and then the RPMs go higher. This happens pretty often... my 05 STi only has 700 miles... am I experiencing problems or is this common?

I would definitely take it in to get looked at. It should not be doing that. The rpms should stay at a constant level.

TAKE IT IN! You have warranty.

It's probably a vacuum hose that got loose...don't do the work yourself though...make your warranty work for you!

I have a 98 1.8L protege 4EAT that was doing the same thing. I changed my transmission fluid the past weekend (drained/filled/drove around/drained/filled again) and took out the throttle body and cleaned it. The car has been VERY smooth ever since. Don't know if it's the transmission fluid or the throttle body. I cleaned the throttle body because someone from a protege board had the same problem and was fixed after cleaning the throttle body. My throttle body was pretty 'bad'. Good luck with yours!

Leo