I have a manual 2006 subaru outback 2.5L XT that idles rough pretty much all the time and the rpm gauge fluctuates at stop lights between 500-1000rpm. The car also stalls at low speeds and almost always about 1/2 a mile from my house when the engine is cool and at a stop sign or light. It seems to not do it as much when the engine is warm. No mechanic can figure out what it is yet. Gas mileage is getting bad because of it, check engine light is on. One mechanic thought then an engine coil because there was a misfire in cylinder 4. He switched that one to 3 to see if it would throw the check engine again and it did not. Then they thought it was the fuel injector because they were switched and now they are back to normal. Now they think it is a head gasket. Any help?