2003 Dodge Intrepid Timing

I just recently changed the water pump and timing chain on my 2.7 L '03 Intrepid. The marks on the new timing chain are lined up with the marks on the cam sprockets and the other colered link is between the mark on the crank shaft and oil pump. As far as the timing marks go, I believe it is just as it was. It will start but is very sluggish and will not idle. Every 15 seconds or so it backfires. Other than the backfire there is no other noise (ie. I don't think there is any internal engine damage). The cam sprockets were not moved more that 10 degrees during removal and re-installation. The old chain was stretched a bit. I am stumped. What else can I do?

Also, check engine light has come on but I am not able to obtain the codes as I don't have a scanner. Is there something else that could be causing the backfire?