Back story...Picked up 02 Neon with known transmission issues. Ran but didn't move one owner 184,000 miles decent shape. As transmission issues meaning it didn't move but it felt as if it wanted to.

Ok now what I've done changed out trans filter and now seemed to shift fine threw all gears even drove it to town as a tester run and back home. As soon as I pulled into the driveway it popped a check engine light and started backfiring thru the airbox random idle between 1000 to 3000 and terrible shifting.

Now I've read the chilton from front to back and I'm still flustered can not sem to figure anything out on my own so please give me some feed back. I don't usually go to the computer as I don't have much time but I need help.