Rough idle when warm

There's a wire going to the charcoal canister? What would that be for?

For the idle issue, has he checked for vacuum leaks?

I have no idea what the wire is for other than a sensor or solenoid. I haven't looked at the car yet and we have no manuals or diagrams yet...hope to get a GM manual in a day or two. After his mechanic disconnected the wire it runs fine....but why? That's what I'm asking you guys for. Thanks

Does the car have Federal or California Emmissions package? What is the engine vin code? Charles

Just a thought. Maybe he's talking about a wire to a solenoid that opens/closes vacuum to the canister for emissions. Is it possible that he's got a leaky hose or something to that effect? Could be the problem is a vacuum leak (as someone else mentioned) caused by leaky emission hosing. Removing the wire could be taking the that emission system out of play. Good luck. Drink