2012 JGC 3.6 rough idle - JeepForum.com
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post #1 of 18 Old 10-07-2018, 09:45 PM Thread Starter
Blackshirts
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2012 JGC 3.6 rough idle

No codes thrown.

Started a few weeks ago. Thought maybe bad gas.

No problems with acceleration or driving at speed. Only when stopped at a light.

Rough. NOT about to stall. Just not smooth as glass as normal.

Anyone else have this happen???

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post #2 of 18 Old 10-08-2018, 07:08 AM
BigTizzie
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My guess would be worn spark plugs or plugged fuel injectors.

Had it on my 2005, tried spark plugs and IAC valve. Didn't help.

Clean throttle body with that special spray? Plugged air filter?

I have 4 bad spark plugs right now and the idle is fine. Got the spark plugs and intake gaskets coming from RA.
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post #3 of 18 Old 10-08-2018, 08:48 PM Thread Starter
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71k miles.
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post #4 of 18 Old 10-08-2018, 11:59 PM
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Usually this is a small vacuum leak somewhere, like the brake booster check valve, or an O2 sensor getting tired. But there are a ton of things that can cause this, like cam phasers, or worn lifters, or burnt valves, or carbon built up in the throttle body, plugged air filter.
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #5 of 18 Old 10-09-2018, 06:23 PM Thread Starter
Blackshirts
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So wait for a code Im guessing. Im not going to spend all the time and money replacing parts.

Its not that bad. Just not smooth as glass like it normally was.
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post #6 of 18 Old 10-10-2018, 05:27 PM
danelo
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Maybe you have a bad motor mount. I just changed the mounts on my 2012 and I cannot feel when the motor is on, where as before I could feel the motor at idle.
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post #7 of 18 Old 10-10-2018, 06:22 PM
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Good point

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #8 of 18 Old 10-10-2018, 08:40 PM Thread Starter
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i'll check them!!! great intel!!!
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post #9 of 18 Old 08-07-2020, 11:41 AM
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Question

Approaching 198k miles so...

Rough idle for me. I am not getting any codes.

I haven't changed the throttle body yet. Is this an OK idea? Will it help?

Which one?

I have done the plugs. OEM ones 10k ago on the easy side. 20k ago on the tough side (drivers).

Just trying to get in front of this before $$$$$$$.

I have been using Lucas fuel system treatment the last few tanks.
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post #10 of 18 Old 08-07-2020, 12:17 PM
ColdCase
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I'd carefully check for vacuum leaks, especially the brake booster check valve. Changing the throttle body won't hurt, may help. What about the PCV valve? Just about everything else is $$$$ that you probably won't get in front of.

So have you tried different fuel and is it the right oil for the engine?
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #11 of 18 Old 08-07-2020, 02:39 PM Thread Starter
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How do you check the break booster valve for a vacuum leak?
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post #12 of 18 Old 08-07-2020, 06:58 PM
ColdCase
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The safe way is spray soapy water along the vacuum hose, vacuum check valve, and intake manifold fitting. If you see bubbles or water being sucked at any spot, or the idle changes, you've found a vacuum leak.

The early model boosters can rust, there is a couple recalls on them. If you have noticed the power brake performance/feel has changed a bit, you could have a bad booster.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #13 of 18 Old 08-08-2020, 12:36 AM
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I did have the brake booster recall done last year.

Checked the vacuum lines around the booster, engine etc. Seem good. Not brittle at all.

Not really rough idle.
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post #14 of 18 Old 08-11-2020, 11:31 AM
Bilko
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Is it a rough idle or just a slow idle? Try shifting to N when stopped at the lights, if this solves the problem you may just need to change your AT fluid. The 5 speed transmission can drag the idle speed down when the fluid ages.
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post #15 of 18 Old 08-14-2020, 07:40 AM
steve_wwk2
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I recently was experiencing a rough idle at stop lights on my 2011 3.6, checked under the engine and noticed lots of what looked like hydraulic fluid. It was a busted motor mount on driver side. Replaced both sides and solved my rough idle problem.

2011 Grand Cherokee Laredo, 3.6L
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