New to me Acadia. Only code I am getting is P0300. 149000 miles. I don't know the history on the car. Will start and run. I drove it 10 miles to my home. Handles nice but runs poorly. It makes a rattle for a few seconds. Misses very hard at idle. I am going to assume this is a timing chain issue from all the other posts and videos I have seen. I just hope there is no bent valves. Seems like I would have other codes if the timing chain had jumped.