I have a 2005 magnum RT with 119,000 miles, she ran great no issues until one day I went to start it And it fired up and then died. I thought that was odd and fired it up again and boom normal I played it off as “I must of let the key go too soon” , didn’t have any issue again until a week later it did it again and this time when I tried to do it again it started up but was struggling to stay with a really rough idle rpm falling to almost turning off then rev itself up and then drop back down Over and over at the same time I have the lightning bolt and bas light flashing with a dead gas pedal so if I tried to give it some gas by pushing the gas pedal nothing will happen. If I left it rough idling and struggling to stay on until the engine warmed up and then turned it off and back on the car would work normally again. Sometimes though the car doesn’t even stay on and rough idle no matter how many times I try and start it, all it keeps doing is firing up and die firing up and die. I changed the throttle body out and after 1 session of rough idle with the new throttle body the next day the car fired up perfectly and ran good for about a week then I changed the spark plugs out and boom later that day problem came back. I did the “key dance” and the only Code I’m getting is P0643. This problem is really inconsistent and I can’t figure it out please if any member has any idea what it could be or has gone thru something like this with there car please share any tips would be greatly appreciated

here is my car exactly what it’s doing

 

Drop by an auto parts store and have them put a scanner on it to make sure you aren't getting any more codes.

 

It sounds like a failing fuel pump if you have the original one in there. However, before you drop the tank and spend all that money, try swapping the fuel pump relay with another, known good, one. I had a pickup with a new fuel pump doing this and it turned out to be a bad relay. I think a new one was $20 back then.

 

Don't drop the tank on a Magnum (or any LX) to get to the fuel pumps; they're under the back seat. P0643 SENSOR REFERENCE VOLTAGE 1 CIRCUIT HIGH is a sh!tty code because it isn't specific. Definitely put a scanner on it to see if there are any more, but the symptoms you're describing sound like low voltage/dying battery. I can tell you from personal experience that once a battery under load hits 11 volts in these things, everything starts crapping out. Extremely sensitive to voltage and power fluctuations. Get your battery tested at minimum, maybe your alternator too (if it isn't putting out at least 14 volts at idle).

 

My 05 RT did some of the same thing yours has done about 2x, no codes. When I did drive mine and had to stop at a stop light, or drive through. It would cut of as if you cut the switch, no codes. Most of the time it would restart and I could drive home or wherever I needed to go. My mechanic, kept it and drove with scanner attached. Nothing happened while he had it. We replaced coil packs, cam or crank sensor, spark plugs, and the recall on gas tank. I chose to replace the PCM, as mine had over 150,000 miles on it. PCM was replaced over 2 years ago and I haven't had another issue with this kind of problem. Hope this helps, good luck.