1991 mustang 2.3l losing power just wanted to know why?

ignition module or stator in the distributor..

Agree with what MK says on the mass flow sensor, however having a 1991 2.3L (in a Ranger) I've found the fuel filter will clog and starve the engine. The ethanol in today's fuels frees up lots of deposits and debris accumulated over the years. When first introduced on the supply side, debris appearing like small pieces cellophane were initially freed. For the cost, it's a cheap thing to try, and good maintenance anyway. I change mine every other oil change.

I also use NAPA Gold, as cheaper filters have glued-together (vs. spring compressed) internals that can separate. You don't want filter failure resulting in debris making it to the injectors.

Best wishes on your 2.3

being that the car is injected and there is no carburetor the valve thing isn't it. i agree with the ignition and distributor answer but also add that you might need to clean the mass air sensor .. is there a check engine light on or not. if so get the codes check and that might give you some help .

Power valve in the carburetor.