1996 Mercedes Benz 280 Runs rough

Hi, I have had this car for about six months. The engine light has been on for almost as long. I was told that it may be the Mass air flow sensor, so I changed it. I had the engine light reset and it came on again. So I just drove it like that for the past four months. But just the other day it started to run real rough. The idle was a little erratic, and it almost seam like it wants to stall some times when idling. When I am going down the road and try to accelerate it bogs down. Someone told me to replace the plugs which I did as well as adding a fuel cleaner additive. But it did not make a difference. Then someone told me that it may be the o2 sensor which I have bought but will need a mechanic with a lift to install. Do you think that is the problem or is it some thing else. Sorry for such a long question, I just wanted to give you all the information.

Thank you,

Mike