I agree with the poser that said the main harness. These vehicles are notorious for substandard materials and workmanship.
I used to work for Corporate and what I found to be effective is a compound called Stabilant 22. I purchaced it at Carquest, but most MAJOR auto parts stores can get it. It is pricey(about $80 for a visine sized bottle)
but a little goes a long way!!! Brush it on the connectors at the coils and main harness connectors. It enhances the conductivity of the cheap connectors Daewoo uses. I have fixed a lot of GM-DAT products using this stuff and it really does work!!
Follow directions and that bottle will last for a good long time. Good Luck!
