What would cause rough idling?

Vacuum leak or possible low compression on one or more cylinders, eirher will smooth out with throttle.

could be moisture in fuel system. try add fuel stabilizer to next tank. also may want to treat with fuel system cleaner(ethanol treatment specific). have diagnostic run. looking for exhaust issue, cat. conv. specifically. may also want to add oil stabilizer on next oil change to recondition seals and cylinders.