CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2015 Jeep Grand Cherokee Rough Idle (3.6l v6)

Good evening all!

Since December 2019, my 2015 Jeep Grand Cherokee has been idling pretty rough. It first started as a slight vibration but now it seems to be like an electric massager! Some days are better than others, but I havent been able to find a pattern yet. The only rough pattern I have is that it tends to idle better in cooler weather (40’s) than warmer weather (50s +).

I’ve always kept good and timing maintenance with this car so I was pretty frustrated to see this issue develop. I took it to the dealer and after some time, they came back and said the BCM was bad and it needed to be replaced before they can do anything as they can’t get any readings off the cars engine. After $700 later, they could connect to the BCM, but didn’t find anything unusual. And with perfect timing, that day I brought the car in, the idling issue wasnt that severe.

So after a week of the issue getting worse, I decided to take a look at the engine for myself to see if I can spot any issues, and oh boy did I spot an issue! The air intake was disconnected from the engine block! I could see the butterfly valve and everything. This immediately set me off as it would have been deliberately taken off, but from my visits to the dealer and other shops, at no time should that have come off. There’s been no major engine work done to the car. The BCM was installed under the passenger front airbag. Perhaps they also wanted to look around the engine? But this is something that doesnt just pop off, the metal clamp was loosed as the blue markings were no longer aligned.

Timing wise, I am not sure how long it’s been off. It could be 4 months, when I first noticed the issue. Or just a week from when I picked it up from the dealer.

So my questions are:

Should I be concerned with dirty air flowing into the engine long term (I’d like to drive this car into the ground)?

Could this be the root cause of the rough idle issue?

Any advice for some ways to maybe ‘clean’ any deposits that may have formed from the dirty air brought into the engine.

Thank you also much so much for the help in advanced!

Without that hose connected, the Mass Air Flow sensor wasn’t providing the computer the proper information so the engine could run properly.

So yes. It can cause an idle problem.

As far as the dirty air entering the engine, that’s water that’s passed under the bridge.

Tester

Hi Jonathan,
I too have a 2015 Grand Cherokee 3.6 with a vibration at idle. Like yours, mine also idles smoother in colder temps. Overall, my GC runs great but the rough idle drives me nuts. I replaced the plugs (which is a total pain in the butt) and I’ve just replaced both motor mounts and transmission mount… the rough idle still persists. My mileage is at 75K. Just curious, Did you ever get your vibration problem resolved?
Thanks,
Paul