2005 Mercury Sable LS Premium 

133000 miles

Automatic/No OBD-II codes

Hello, Scotty!

My 2005 Mercury Sable has engine surges at idle where the RPM drops about 100-150 RPM and goes back to normal and gets about 3x worse with the air conditioner on. This happens constantly every 5-10 seconds. It does still surge even with the air conditioner off and when AC is on it still blows very cold so AC seems fine. Also, once the car starts to get going it drives good, only problems are when I'm stopped. I've replaced all the spark plugs, problem coils, and the idle air control valve. Problem persists. I guess next would be my MAF sensor? Please let me know your thoughts. 

Thank you, 

Eric