94 marquis problems

my marquis has some big problems, and i really need help cause everybody i have taken it to has no idea what is wrong, hope you can help. it backfires, and jerks back and forth, on acceleration but it also does it whenever you drive down the road, really bad when pulling the hill.

What's been maintained recently, what hasn't been?


Plugs, wires,
PVC valve,
fuel, oil, and air filters,

Pluged catalytics?
Bad batch of fuel?
Vacuum hose fell off?

check spark plug wires, the set up could be wrong. Make sure the wiring is correct.