When to change the timing belt on 2005 grand prix

The 2005 pont, grand prix, doesnt have a timing belt, rather it has a timing chain, this chain is good for 150,000 or more miles.

The owners manuals are pretty general in respect to this particular item. You should have it checked at 50k and every 25k miles after that. It should be replaced if you see any signed of wear or Stretching. Your problem may just be a matter of a plug has fouled or you picked up some less than desirable fuel at one of your stops to refuel.