2000 neon backfiring

My dodge neon 2000 is backfiring i think, when I am at a light, it wants to die. Engine runs shakey, when i take off it has no power and makes a noise, my husband believes its backfiring. He just changed the oil in it and then changed the spark plugs. he then later realized he had too much oil in it so he took a quart out, he thinks the spark plugs may be fouled now cuz autozone told us there is a oil and gas in the combustion chamber?? that the spark plugs need to be cleaned and the problem will resolve it self by drying out?? but i believe it was starting to make this noise(backfiring??) before he even changed the oil?? so im not sure if its because he over did it with the oil change, i think it was backfiring before, ughhhh! anybody got an idea?

Is the check Engine Light on (CEL) ?
Any local Auto parts store can pull the Diagnostic Trouble Codes (DTC) for free.
Bring DTC's back to your Thread in AF.

You are probably getting a misfire and raw fuel is being dumped into your catalytic converter causing the backfire.