98 400l xplorer..runs good in weather above freezing..20 degrees or less gas line freezes up..already had put isop. in before using..ran fine for about 30 min. shut it off..then would not start.. put in heated garage for a hour and it fired up..starts up idles fine and in about 10 min. it will idle about twice as fast as normal when its out in freezing weather..

 

Don't like Heet or any product like it,but some do. Sounds like it's running lean also.If you're running the stock 200 main,30 pilot,you might think about bumping them up until warmer weather. Plus cold weather's hard on seals and gaskets just as much as hot weather. Could be sucking a little cold air. You can spray contact or carb cleaner around the intake and gaskets when it's idling high and see if the rpm changes. If it doesn't then could just be needing jetting change or possible crank seal leaking.Seal behind the drive clutch is usually the main culprit on seals.