Diagnosing a Rough Idle

[dahbears27]

Hi all.

First time poster and Gladiator owner. I want to start off saying I really enjoy my 2020 Gladiator Rubicon 3.6l, but a rough idle has been driving me crazy. I bought the truck used at the 52,000ish mile mark beginning of this year. I don't think I noticed the rough idle during purchase. Current mileage is about 64,000. The rough idle is intermittent but occurs and is most notable in most starts from cold and some of warm starts. I have a Tazer installed (by me) to bypass the security module, and subsequently auto start/stop, to allow me some more diagnostic freedom.

Generally here is the symptom flow and extra details:

The start is smooth, no excessive ticking or noise as the oil pressure comes up. No unusual ticking even while the rough idle is occurring. I am currently running 0W-30 Amsoil SS. 0W-20 Amsoil Extended Life on the previous change as soon as I returned from the dealer. As the idle RPM comes down it's still smooth even around the 750-850 mark. But as the idle drops down to its lowest, 650-675 I believe, a deep rumble/vibration can be felt and heard. It comes in short waves/surging. Smooth then rough back to smooth etc. Thankfully, the sensation has NOT changed e.g gotten worse. I want to check all I can before God forbid I have to divert to a dealer.

Here are the things I have checked so far. I would love some more suggestions:

- Fuel: I normally run 87 octane however I have been testing a couple tanks of 91. I cannot notice a difference so far. I also have used multiple stations to rule out fuel contamination.

-Ambient Temperature: I really noticed the rough idle at first in February. Its July in NE and the idle is still odd. So even with summer fuel and warmer ambient temps there isn't a difference.

-Fuel Economy: Compared to when I bought the truck and now I actually have gotten better mileage, likely summer vs winter blend, However I track all fill-ups manually and have seen no discernable change or degradation.

-Misfires: Some other threads about rough idle and the classic Pentastar cam failures indicate that higher than normal misfires on the passenger side cylinder bank can indicate issues. Using JScan after my 30 minute commutes, multiple times, has resulted in readings of less than 10 misfires on any one cylinder during the drive. My drive includes a few stop lights and spirited accelerations to get up to speed for the interstate.

-Throttle Body: I disassembled and cleaned the butterfly during my last oil change. Even though it had some oil deposits it wasn't filthy.

-Codes: I have had no engine or related codes while I have owned the vehicle. I've also checked for stored codes and none are present.

-Oil filter: I cut apart the last filter and checked for metal and was able to spot no noticeable flakes or debris under good lighting.

I hope these details can give someone with more experience with this issue some idea of other things to check. I've had far too many dealers burn me so I'm definitely "dealer adverse" I have access to AlphaOBD and JScan. Any ideas are much appreciated.

Thanks!

Sponsored

 

[swtrailboss]

Check your motor mounts…..if you don’t see anomalies in the misfire category then it’s more likely a vibration issue you are experiencing as a “rough idle”……..any lifts or aftermarket parts installed prior to feeling this issue?

also check your fuel trim ST and LT and see if they seem out of range.

 

[dahbears27]

Thanks for the reply. Hmmm…I’ll make sure to check the motor mounts. This is a dead stock Gladiator. I have read about potential software updates for this issue but haven't confirmed anything. Doesn’t look like there are any recalls open for my truck either.

 

[Bandit’s Lair]

Has it ever been off-road? Maybe at an extreme angle and gotten any kind of blow by smoke? Did any “event” happen prior to you noticing these low rpm vibrations? Do you use any kind of additive before oil changes or in the fuel tank?

 

[dahbears27]

Before my ownership I couldn’t say, but considering I was the person to put the first scratches on the skid plates, not likely I guess. I took it off-roading in the Branson area once back in March. There were some steeper climbs and obstacles but I never observed any blow-by smoke as far as I can remember. I do recall feeling the vibration in the hotel parking lot but can’t remember if it was before or after unfortunately otherwise it ran and runs great.

 

[Bandit’s Lair]

Ok. I was just spit balling trying to think of what could cause a low rpm vibration and you mentioned a few misfires. I’d look toward plugs but 52k seems way early to need em. I always run a bit of Seafoam in the oil about 150-250 miles before my oil changes to clean up and possible deposits. The rest goes into the fuel tank to upkeep injectors. It’s worked for me through 6-8 vehicles and about 25 years or so.

 

[dahbears27]

No problem! I’m about 5 minutes from pulling the cam position sensor on the passenger side to see if it has metal on the cam encoder wheel. Unfortunately that was a grim sign on my wife’s ‘14 GC, even though it was an earlier Pentastar.

 

[Mojave20]

Might be worth it to replace your plugs. I have a 2020 and replaced mine a few months back at 50k. Had an intermittent rough idle and pinging a low RPM. This is what my worst plug looked like.

 

[dahbears27]

Goodness that is rough looking. Definitely need to check the plugs then. Do you remember what size that particular plug was from? I figured out how to get a good log of my fuel trims, just need to catch the idle acting up. While practicing getting my log to work I was idling at a little over 150 oil temp and the idle was basically perfect. Also attached was the encoder wheel via the cam sensor hole. It had a little metal but not too bad.

Sponsored