2001 sunfire engine problem
 

hey everybody. I am here in hopes of assisting my girlfriend. She says that when she is driving her 2001 sunfire at normal speeds (50-60 mph), the vehicle drops from running on 4 cylinders to 2 cylinders and begins running terribly. This also occurs after the vehicle has been idling. We are trying to get it ready for selling, and I don't want her to sell garbage. Any insights would be great. Thanks for any help.