1995 Hyundai Accent air/fuel correction

I took my car for a computer scan because I'm having problems with it. While I'm driving it wants to stall and looses power all the sudden, I have to press the gas all the way to the floor in order for it no to stall (die) Now the result came out as he following DC
TC CODE 81 AIR FUEL CORRECTION, they don't really know how to fix this problem they recommended a tune up to see if l that would fix the problem but they were not sure or maybe check some or change some sensors. Can anyone please tell me what I should do. Also a full tank of gas only lasts a week when it used to last 2 weeks and finally when I have the heater on I smell a really weird smell like carbon monoxide or somehing like that I have to keep the windows down and the heater on. Please help