I second the replacing of the vacuum canister and that nothing goes on those ports. Just a filter cap and I'm not sure it does anything. My issue. years ago, with my cruise, was the servo. The wire coil had become "unspun", and broken. Not sure how that could even happen, but it did. I found another one at the junkyard, and it fixed it. I believe, there are some cruise servo's off of other GM cars that are identical to the Fiero one.
Edit: Servo is the correct term, not solenoid.
[This message has been edited by jimbolaya (edited 10-26-2014).]