My 98 dodge neon's speedometer started jumping up and down while driving, then the air bag light came on and stays on, next the car started making a puttering noise and sounds kinda muffled when shifting gears and it gets worse when shifting to higher gears, next the service engine light came on and stays on, I had it hooked up the box thing at ADvance and the guy said his reading says po204 injector circuit open cyl 4 and po304 cyl 4 misfired....so we replaced the plugs and wires but after that the lights are still on and then car still sputters PLEASE HELP??????

SOURCE: Intermittent Misfire on cyl #4 1997 Buick Lesabre

How's your coolant level? The intake manifolds on the 3.8L engines are prone to breakage at various locations causing coolant leaks into the crankcase and vacuum leaks on intake ports.Removal of the upper intake manifold will be necessary for inspection. Also, check for vacuum leaks at various locations on the outside of the intake manifold using WD-40 or brakeclean/carburetor cleaner sprayed hoses, non-electrical components, at the base of the manifold etc. As for a faulty injector, not likely but if you suspect one you can always swap the suspect injector with another on the engine and see if the misfire follows the injector. Just be sure to relieve the fuel pressure before servicing. Hope this helps.

SOURCE: i have a 318i 1998, the engine light came on. i

Sounds like it may be running a bit lean - do basic checks for air leaks in the induction system (such as leaking manifold gasket, loose hose fittings to air flow sensor etc).
Condition of HT leads also worth a check.

SOURCE: 2001 grand am 2.4L code PO304 cyl 4 misfire

This could be that the coil it's self is going bad or you have a crack on the boot part that connects to the spark plug.

SOURCE: chevy 5.3 po304 engine code misfire

that meens there is a misfire on cylinder number 4

SOURCE: 2000 dodge truck code po203 po204

p0203 injecter circuit malfunction cyl #3. p0204 injector circuit malfunction cyl#4. po138 02 sensor circuit,high voltage cylinder bank no.1,sensor no.2