I have a 2012 Dodge Durango R/T, AWD with a 5.7 hemi. 165k miles. My father bought it new and I bought it from him with 110k on it. It has been a great truck and has been maintained well. About 6 months ago it started to stumble at idle a little bit. I would have bet a good chunk of money it was a missing cylinder. So I scanned it and found no misfires, no codes, nothing. I thought I may have had a bad tank of gas. Ran two tanks of non-oxy through it with no change. It was due for plugs anyway, so I put a set of new NGK iridium's in it - No change. Then I replaced the PCV and took the throttle body off for a cleaning - No change. I have a professional fuel system cleaner setup, so I did that next - No change. I started to notice it was worse at startup and worse the colder the outside temperature, so I thought it might be the intake gasket. I replaced that with no change. Next I changed the MAP sensor with no change. A friend with a Charger had upgraded his fuel and ignition at 35k miles, so I purchased his coils and injectors for a song, doing them separately with no change.
The idle is definitely worst when it first enters closed loop operation. It feels like a missing cylinder right away. The quality is worse the colder the air temperature. It does get better as the engine warms up, but it needs to be REALLY warm to get where it is barely noticeable. As in about 45+ minute drive. It does get progressively better during that time. Once fully warmed up, it isn't too noticeable. Only a person who knows cars well could tell. My wife cannot feel it unless I point it out. I have a basic scanning app (torque PRO) and the vacuum, af trims, etc. all seem reasonable. There are no codes or misfires. I am starting to suspect I may have a lazy O2 sensor, but I am not sure how to validate that. I just notice that the bank 2 upstream sensor does not seem to move as often or as much as the bank 1 counterpart. The downstream O2 sensors seem to move pretty much in sequence.
I have scoured and posted on so many hemi forums it isn't even funny. At 165k miles, I am more than fine replacing all the O2 sensors, but I also don't want to keep firing parts at this without really understanding what is going on. TIA to anyone who can help!!
Those hemis are famous for roller lifters that wear out and begin to eat the camshaft. Pull off a valve cover, have someone spin the engine over and look at the rockers. You will probably see that they are all not moving the same as they should. You need to pull the heads and replace the cam and the roller lifters with higher quality parts.
Wouldn't that be more consistent and not be affected ambient temperature? I have put about 10k miles on it since it started and it hasn't gotten any worse. I did consider the cam, but given the somewhat erratic nature of it, ruled something out like physical failure
From your dad I would say try the sensor praise that because of not those hemi engines and notorious for wearing out the cams and it will start acting erratic when the cam start to wear
What does ambient temperature have anything to do with it?
If the temperature is above approximately 85°, it normally will idle just fine even when the engine it's not up to operating time. The stumble gets progressively more pronounced and happens more consistently the lower the ambient Air temperature gets. That is why I suspected the intake gaskets - I thought that air was getting in there while everything was cold and was ceiling back up as the ambient Air temperature was warm enough or the engine got warm enough to expand everything.
I guess that is possible. Spray cleaner around the intake manifold while it's running and see if there are any vacuum leaks. I am still going with the bad lifters and cam as the 5.7 Hemi is famous for this problem.