Cylinloid or Solenoid?

I have a 97' grand prix GT supercharge. my problem is this: When i am driving my car my digital read out that tells me how mant miles i have left to go fluctuates up and down and after driving for a while i feel hesitation and sputtering when i press on gas. The car never shuts off on me but i feel i dont have the power i used to have.Had diagnostic done and they said it was a pressure control cylinoid but i could not find this part in part stores. need to know if i am looking for the right part and where to find it. Thank you