My 96 Outback 2.5,  hesitates when i have the a/c on , the idle and acceleration is sluggish. i  have replace many components and also knock sensor , MAP sensor , clean the IAC, replace the fuel regulator valve and  EGR valve.  I don't know what to do next , I just bought park plugs wires and plugs . The funny thing is when i turn off the a/c the car runs fine. May be i'm missing something?

It may be normal. Turning on the A/C on a 4 cyl. you can feel the load it puts on the engine. Can you feel an increase in power output when the a/c cycles off and on? If you know someone with a same model car see if you can compare it to yours.

Thank you very much for your reply. I will check with others and ask  if they experience the same or similar symptoms.