The belt tension on the newer engines is just a spring, on the idler. SO... if it seems lose, you may need to replace the spring. There is a grease nipple on the pivot, and a pump of good waterproof grease should be part of your winterizing. But, if it's sticking... I wouldn't just put grease in it. I would take it apart, and make sure there isn't any old, hard grease, or rust on the shaft. If it seems free... then give it a pump, and see if it helps.
FYI... there is a 3/8" hole that you can stick a ratchet extension into, and release the pressure on the belt. It may free up if you take the belt off, and work the idler back and forth a few times. Also... if the belt is old... it could just be stretched out.