p0016 code
 

need some help with this one sisters car a 2007 cobalt had a timing chain issue it wouldn't start and it appeared that the chain jumped on start up. wasn't something I had time to do so took it to a shop they put in a kit. I;\'m not sure all what they did, but after it ran fine a few weeks later it happened again on start up. They picked it up and said they fixed again it ran fine again for 5, 6 hundred miles now it's idling really bad and is setting the P0016 code help please thanks

Find out what parts they replaced. Maybe they didn't replace the tensioner and it is working it's way loose. Sometimes they look good but don't perform well when in use.