I have the same problem, never really bothered thinking about it much until now. I always thought it could be the clutch hanging up at times.

 

I need to check into how to do these things...Mine shudders if I dont keep the Rs up while taking off.

 

That sounds more like you aren't synchronizing releasing the clutch with applying the gas as smoothly as you should, that's not an issue with the car. To the OP, as mentioned cleaning the IAC and MAP should help some... but most s2ks seem to shudder every now and then when dropping to idle. As long as it doesn't stall out, it's nothing more than a nuisance.

 

Had the same problem it would shudder where i thought it was gonna stall at times. Just cleaned the IAC today all better now