Engine idle too low. Stumbles sputters on startup after sitting overnight. Rougher idle when AC is turned on while ideling it fluxuates.

I have a 2005 ford tauras 3.0l v6 auto ohv engine. Sometimes on start up car stumbles and sputters for 2 or 3 seconds or if you hit the gas pedal right away it clears up immediately. But once car runs for a minute the idle drops close to 550 to 650 rpm and kind of barely fluxuates. Then if you turn on ac before driving it bogs down for 2 seconds and causes a rougher idle condition. No check engine light is on. It just seems it should be ideling around or close to 1000 rpm not 500 to 700 rpm. What are your thoughts?