my inlaws have a 2002 chevy cobalt 2.2 i went over and scanned it the code was P0304 #4 cyl. misfire i pulled the plugs which #4 was tight and the other three were threaded loosely i installed new iridium plugs (OE) cleaned the throttle body and cleared the code still runs rough w/the SES light flashing the vehicle has only 8,800 mi. after my test drive the smell of the vehicle was like a burning house what should i start looking at should i loosen up the man/exhaust before the cats and see if the vehicle runs smoother ????thanks

 

According to my computer they did not make a cobalt in 02 the first year was 2005.
Regardless you need to look into the ignition coil