91 Caravan popping thru intake

I just got a 1991 2.5 4cyl automatic caravan that barely runs. it seems to be popping back thru the intake sometimes. not always. it does run rough. it does have an 02 sensor code. i have not started troubleshooting as of yet. just looking for opinions on the popping back thru the intake. ( burned valve(s)? timing? coil? tune-up? all the above? something else altogether?)

Sounds either like a misfiring coil, bad plug wires or a burnt valve. Do a compression test on the engine and if it has a burnt valve you will see low compression on the cylinder where the valve is burnt. If the compression checks out you may need to look at the cam. If there is a worn lobe it can cause a problem like this but that is doubtful.

fixed it. started listening to the engine a little closer, and it sounded like it was something in the top end ratling around. took off the valve cover and lo and behold, a rocker arm was off. broke the cam loose and put the piece back on. runs fine.....