2006 RAV4 idling rough

Maybe it's just bad gas

My Wife drives a 2006 RAV4 Sport (6 cylinder), probably close to 50,000 miles

All routine maintenance is kept up.

Just recently drove it from Mid Michigan to Wisconsin and back- no problem.

But just since we've been back - and only while idling- it runs rough, like it shakes like it may stall or something.

Drives around town or the highway just fine, without hesitation.

Wonder if I could put some fuel additive, or drive the gas tank down some, and put some other gas in it, if that might do it ?

Never happened before. All plug wires seem fine, nothing looks out of place under the hood, no tell-tale signs of drips etc in the driveway or on the bottom side of the vehicle.

Thoughts on what it might be ?