1999 Neon, my wife lost the gas cap and ran it for a couple of weeks like that before telling me, this may or may not be related to the problem. The car starts fine but as it warms it runs worse stumble on acceleration, backfire through intake, loss of power. sometimes seems down on a cyl. idle seems good, service engine light flashes during hard acceleration but stays on the rest of the time. I have swapped the ECU , removed and cleaned EGR (was clean and ok already). Cat. converter not plugged. I have also swapped out the coil with another used one and I drove it and all seemed ok. The next day my wife informed me the the problem was better but still there. Perhaps I swapped 1 bad coil for anotherbad 1? any ideas ?

 

To read any OBD codes, do this:
1)Turn the ignition key ON-OFF-ON-OFF-ON within 5 seconds.
2)Count the number of times the 'Check Engine' lamp on the instrument panel flashes on and off. The number of flashes represents the code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual codes. For example, flash-flash-flash [pause] flash-flash represents the code 32.

 

did it and got 1-2-4-3-5-5

 

12 - battery has been disconnected within the last 50 key-on cycles (nothing to worry about)
43- single or multiple cylinder misfire (change spark plugs w/stock copper champions and inspect wires and coil pack for any cracks.
55 - end of codes.

 

Please let me know what you find out..... MY car is doing the exact same thing. I just put new plugs wires and coil on it. seemed to help for about 5 minutes but then it started again. My car also smells like it is flooding with gas.

 

Is the code 43 all that you got? What kind of plugs and gap did you use?

 

I used Champion coppers and was told the plug were pre gapped. didn't check. but then again didn't change the way the car runs at all. The plugs that came out were NGK and looked new except for the #1 cylinder was cover in black build up and smelled like gas.

 

Your tube seals may be leaking. You could try replacing the valve cover gasket along with the tube seals to see if that helps. Have you checked your oil for coolant or coolant for oil? Could be a headgasket problem as well.