Cloudy/fogged/hazed up plastic/vinyl windows are cause by wiping them with paper towels. Paper towels are made from pulverized wood products and they impart millions of ultra-fine scratches on the windows every time they're used, eventually building until they turn into a haze/fog. Eventually that will turn yellow from the haze trapping the UV from the sun.
Use either Novus or Meguiars multi-step plastic window polish to remove the haze. Even with the multi-step polish it will still take some serious elbow grease to remove the haze and minor scratches.
Once you've polished the windows to the point you're happy, use only a slightly damp soft cotton towel with lots of soapy water to clean them from now on. Never wipe them when everything is dry. Use an old soft towel, tshirt, etc. Some insist on buying microfiber cloth to wipe them but to me that's not needed and an unnecessary expense.
