Sounds like a faulty MAF sensor since it's a load variant problem. That and you bought a used one. Maybe try cleaning it and also remove your IAC and clean it as well.
In 15+ yrs of automotive repair I've never replaced a coolant temp sensor on a Subaru. They don't fail after or at all.
Last edited by spooln30; 07-05-2013 at 07:22 AM..