2002 Ford Expedition Occasional white smoke from exhaust an

Last week my check engine light came on so I thought I might have bad gas (it has happened before) well I don't drive alot of miles and after filling the car up with gas it still hasn't gone out. Yesterday I was driving and the car kinda stuttered when I was accelerating. It did that a couple of times and then stopped. I went last night and got an oil change and a fuel system cleaning. Well I noticed when the guy started my car a big cloud of white smoke came from the exhaust. The other guy let the hood up put some kind of liquid in and they started it up and no smoke. Today I saw smoke briefly again. I went to Autozone to have them read the codes for the light. The paper they handed me said 1)O2 sensors, 2) ignition misfire, 3)fuel injection problem. Going to take my car to a repair shop, but want to make sure they are really fixing just what the problem is. Any help would be greatly appreciated!