4 Wheel Drive/SUVs: Engine shudders when tuned off, fuel mileage, shudders

Question
I have a 1994 S-10 pickup with a 4.3 liter vortec engine.  I have noticed that it is idling a bit rough and when I turn the key off to shut off the engine, it shakes and shudders very roughly as it shuts off.  The check engine light has come on several times when idling but it goes off when I accelerate.  I had a friend scan it and he got a (code 35-idle air control)  Does this sound like the likely culprit to you?  If so, can you tell me where it is located on the engine.  Also, I seem to get very low fuel mileage, and it doesn't have much power.  It is derivable, but I have always thought that it should be a bit snappier than it is.
Thanks for any help that you can give me

Answer
Brian have you ever tried to adjust the timing on this S10 it seems that might be the problem with it . That would also make it snappier as well thanks ADAM