Dodge Repair Questions? Ask a Mechanic for Answers ASAP
HiCustomer welcome to Just Answer!.
The combination of symptoms you've mentioned often wind up being a broken valve spring, fil. This is something we saw pretty consistently on the earlier Hemi engines and it was something that could happen on a young engine as well as those over 100,000 miles.
What happens when a valve spring breaks is the affected valve can't follow camshaft profile like it should, the lifter pumps up and the valve hangs open. This opens a passageway between the intake and exhaust systems, allowing exhaust gases to be dragged back into the intake manifold where it contaminates the intake charge of other cylinders as well, reducing oxygen intake and causing widespread sooting of the spark plugs. It's most pronounced at idle or low throttle angles when the difference between intake vacuum and exhaust pressure is at its greatest. You may notice improved engine performance overall as you go deeper into the throttle for this reason.
Unfortunately, it's not always easy to decide which cylinder or even which bank is affected. With no codes to work from, it's pretty much a coin toss to see which side gets the valve cover pulled first. The passenger side is easier and tends to see more actual broken springs for some reason, so I'd start there.
You may or may not have hurt a valve with the broken spring. Normally, the spring still has enough length left to it to keep the valve away from harm, but occasionally one does get smacked by a piston. Compression or percent-leak testing of the affected hole will tell you more once the spring is replaced. Some instances will show good compression at cranking speeds when the valve can still somewhat close, which is always good news... but makes it harder to find the affected cylinder from the beginning.
If you have any questions, don't hesitate to write back. I'll be glad to help.