6.4L Hemi Extremely Rough Idle at Low RPM's

[krcaryl]

Good morning everyone. New member and first time poster...2016 Ram 2500 with the 6.4L Hemi with 164k miles. I purchased this truck with 140k miles and up until yesterday, no problems at all. That said, while driving in to work yesterday and out of the blue the truck starts having an erratic rpm issue. The dreaded "red lightning bolt" comes on as well as the check engine light. Fortunately I was able to limp it home. After some internet digging, I surmised that it was a dirty electronic throttle body. Purchased a new one to include a new sensor. Did the swap easy peasy and the "relearn" for the positioning sensor (old one was quite dirty so a good thing either way). Started it up and although the red lightning bolt went away, the truck is still displaying an extremely rough idle, especially at 1,000 rpms or lower. Multiple attempts at "relearning" the position sensor and still no change. Disconnected the battery completely for 30 minutes, hooked it back up, and did yet another "relearn" and still the same. Then checked all visible wiring and connections and all appears to be fine. Was told that the plugs and coils were change around the 100k mark but taking a closer look, I am almost certain they are original. Any chance this could be the culprit? Any other thoughts? I'm going to change the plugs and coils this weekend for piece of mind, just really hopeful this is in fact the issue.

 

[Jeepwalker]

Yes, spark plugs do fail from time to time. I've even, over the years, had a few brand new spark plugs which were faulty out of the box, although that is extremely rare. Hopefully you will get lucky and that will be your only problem. You can look at each spark plug really carefully for cracks in the porcelean on the bottom and top sides, and ohm them out. Usually one would spot a problem visually or by an ohm test.

But there are many other possibilities. Too many to take a scatter-gun approach to (not saying you are). Maybe before you replace them, you might swing by a parts store like Autozone and get a free scan of your truck's computer. That would indicate if there was a misfire and at what cylinder or help identify other possibilities. And you can start there first. Poor engine operation (it might not be a mis-fire) are where a computer scan can really steer towards a problem. If you had one bad plug, or coil, or fuel/vacuum/sensor related, you could target the problem rather than possibly replacing parts that may not need replacing. Computer fault codes might indicate some other 'system' to check into, which should save you a lot of time and potentially, money.

Does the engine run poorly at all times, or just low idle? If you DO plan to pull out the spark plugs, I would pre-plan and perform a compression test of each cylinder while the plugs are out (engine previously warmed up). You could rent one at Autozone or OReilly's for free. This could answer or eliminate a lot of other questions right away. And while you are at the auto parts store getting a scan, have them perform a battery check. And make sure to clean/check the battery and engine grounds (very important). Bad grounds can spoof a lot of other problems and they're pretty much 'cost-free' to make good.

Other possibile causes could be:
- Failed/dirty Mass Air Flow (MAF) sensor
- Poor ground
- Plugged air filter (not likely but worth a look)
- PCV valve bad
- Faulty coil (these fail from time to time)
- Rodent-chewed wire/s & hose/s
- Vacuum leak (cracked hose, failed gasket, etc)
- Drifted engine coolant temp sensor
- Leaking head gasket
- Fuel delivery issue (low pressure or injector, etc)
- Burnt valves
- Bad cam/lifters etc
- TIPM (computer)

EDIT: Added:
- Failing Crank Position Sensor (CPS)
- Water in the gas (would run bad at all rpm's)

 

[Jeepwalker]

There was a guy at another forum where the rubber boot for the air snorkel from the air filter box (a rubber boot at the throttle body) was folded under during a maintenance installation. That essentially opened a crack where air was being sucked in at the throttle body, bypassing the MAF ....throwing off the amount of air the computer was 'looking for'.

Welcome to the forum BTW...

 

[Jeepwalker]

If it were my truck, I would begin by 1) cleaning the battery terminals, and loosen/wiggle the engine and body grounds.

Then I would 2) look over the wiring really well, and the vacuum hoses. Look for connectors which may have fallen off, frayed wires, chewed wires, etc.

3) I would remove the fuse box lid and make sure all the fuses were in place and seemed good (just a precursory look). Just in case.

Then I would scan for engine codes. And get the battery load tested at the parts store. Then report back here what codes you come up with. The reason I would check the grounds and wiring first is a problem with 1 or 2 could be an easy fix, but also a wiring or ground issue could also cause errant codes.

Other forum members may have other ideas where to begin, but that's how I would begin tackling things.