2004 Dodge Stratus check engine light and almost stalls.

My 2004 Dodge Stratus SE has been acting like it is going to stall when at a stop, especially when the heat or air is on, the check engine light comes on and off (more off than on), and the dash lights and headlights flicker when it acts like it is going to stall. It does not do this all the time but more often than not. I did have it looked at by a friend mechanic and he said no codes appeared and he couldnt find anything wrong with it. The spark plugs and air filter have been changed. I read all the other questions and couldn't find one like mine. Alot of them are that their car stalls but mine doesn't. same problem? Any ideas?
Also my blower only works on high but i already got the answer to that, thanks.