I used to think that my a/c was causing this problem until I fixed my low speed fan resistor. Now I notice when my high speed fan kicks on js when my idle drops and my clutch is easy to slip in first gear. Also a major lack of power when moving. Is something wrong with my alternator or pulley? I hear no strange noises. When the fan turns on you hear the engine shudder and it shakes a lot more. When the low speed fan is on with the a/c the car feels smooth again, with not as much of a power difference.

 

Maybe this will help, but I had a similar problem where the idle would drop when turning the wheel (the electric power steering). I read in a post somewhere that the air intake system wasn't optimum. I cleaned the MAP (or maybe mass air flow sensor just after the air intake throttle body) and the problem was greatly diminished. Now only a slight change in idle, when I turn the wheel. It seems that engine load wasn't responding to the need for more power.

 

I'll try it out. I know the throttle plate itself is spotless but maybe that doesn't tell the whole story.