Welcome mate you certainly have your car in much colder conditions than us but you could have a sticking thermostat if you don't know when that was last replaced. Also some subaru upper engine cleaner would be good to use on a car your age for the idle issue. I would check all your vacuum hoses on a car that age and boost gauge line if you have one as well.

Plus check you pcv Valve and catch can set up for and blockages played havoc with my old model. People round here are quite knowledgeable I'm sure you will get some more good advice.

Mark