2001 Other Saturn Models I don't know if it's electrical or

Electrical problem
2001 Other Saturn Models 4 cyl Automatic 156, 00 miles

I have 2 problems with my car, SL1. My service engine light has come on and my OBD2 reader says cylinder 1 misfire. That is the recent one and that light does go out from time to time. The scarier problem is that it's losing power sometimes. On cold/damp days it seems that while im driving the car is fine but at a complete stop or low idle all my light dime, stereo shuts righ off (i do have a stereo system/remote starter in the car but not using the stereo right now with these issues!) And it wants to stall. Once I start to go everything is fine. My voltage reader is reading and charging fine while driving between12 and 14 but at a stop it drops so low the error message comes up and cannot tell me where its sitting. Can't even shift gears sometimes not enough power. Do I need a tune up and new battery (4years old) or would that be a waste of money. I's completely intermittent and I don't have the money to keep bringing it to places to try things. Car has been nothing bu trouble it's whole life. I don't think there are any original parts left!