ISO mechanic- my 2000 expedition idles rough in the cold, basically under 40 degrees. If the weather is over 40 degrees this doesn't happen at all and car runs perfectly. There is no diminished performance when driving. I've had the car looked at twice now. Plugs and boots have all been changed. O2 sensor is fine. Codes don't point to anything specific. I would like for an experienced mechanic to be able to tell me what's wrong. Don't wanna throw parts at it. Thanks in advance!