Shaking at idle

reconeTJ

reconeTJ

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Joined
Jul 3, 2021
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So I noticed that my 2006 4.0 has a little shimmy or light shake at idle every 3-4 seconds, so I decided to replace all the sparkplugs, now the new ones are in and RPM gauge is perfectly still, so no fluctuations. Engine motor mounts seem solid so does the trans mount, I have a new one just in case. Doesn't seem like it's loosing power, runs awesome and nothing else seems to be wrong. And no cel.
I popped the hood an I noticed that the alternator pulley does a little shimmy every 3-4 sec, but that might not be the cause of the engine shake. I don't know what else could it be, I checked everything and all the pulleys seem okay, am I missing something?
 
reconeTJ said:
So I noticed that my 2006 4.0 has a little shimmy or light shake at idle every 3-4 seconds, so I decided to replace all the sparkplugs, now the new ones are in and RPM gauge is perfectly still, so no fluctuations. Engine motor mounts seem solid so does the trans mount, I have a new one just in case. Doesn't seem like it's loosing power, runs awesome and nothing else seems to be wrong. And no cel.
I popped the hood an I noticed that the alternator pulley does a little shimmy every 3-4 sec, but that might not be the cause of the engine shake. I don't know what else could it be, I checked everything and all the pulleys seem okay, am I missing something?
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Random thoughts:

Is this when in gear holding the brake?

Does it happen before and/or after the engine is up to temp?

AC on? Blower fan on high? (Do symptoms change under different loads?)
Exhaust isn’t touching the lip of your transmission pan?

Transmission mount is OEM?

You stated that your engine and transmission mounts seem solid. Have you torqued them down to verify they aren’t a cause?
 
More random questions:

What is your engine compression?

What are your rpms in idle?
 
A/C or blower fan stuck on as @Mikee024
Mine did this and I found the A/C was kicking in and out when it was off so I put my A/C on full for a few mins and it has never come back. I am sure even my problem was deeper but it worked.
 
P man said:
My vote is trans mount
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I would definitely ensure it’s OEM, in good condition, and properly torqued.

Although, if this was the cause, it seems a little odd that the idle shake only happens every 3 or 4 seconds.
 
reconeTJ said:
I popped the hood an I noticed that the alternator pulley does a little shimmy every 3-4 sec
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Not to pick at the exact words but it might be helpful. The alternator pulley shouldn't move or shimmy at all, just rotate. The tensioner is below the alternator and that arm bounces up and down a bit as load changes on the belt. Odd movement in the alternator pulley is a problem, movement in the tensioner as load changes isn't. If the A/C is cycling which might happen every 3-4 seconds you will see and hear the clutch click on the A/C compressor and the pulley turn. It can go on in defrost as well as the cool settings.

A little miss at idle is really nothing much to worry about if everything else is okay and there are no codes.
 
pagrey said:
Not to pick at the exact words but it might be helpful. The alternator pulley shouldn't move or shimmy at all, just rotate. The tensioner is below the alternator and that arm bounces up and down a bit as load changes on the belt. Odd movement in the alternator pulley is a problem, movement in the tensioner as load changes isn't. If the A/C is cycling which might happen every 3-4 seconds you will see and hear the clutch click on the A/C compressor and the pulley turn. It can go on in defrost as well as the cool settings.

A little miss at idle is really nothing much to worry about if everything else is okay and there are no codes.
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In a perfect world it wouldn’t bounce but with the belt acting like a spring and loads changing I’m not surprised that the tensioner moves. Mine moves as well.

I also get small vibes in idle (sometimes more than others). Otherwise, my engine doesn’t pop codes and drives well.

I’d like to solve my vibes as well, but I agree with @pagrey that your engine could be fine if your only issues are small vibes in idle.

Let me know if you solve it!
 
Mikee024 said:
I also get small vibes in idle (sometimes more than others).
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Some people like @Irun have had good luck smoothing out the idle cleaning out their injectors. From what he described just pulling them out and spraying them down with some carb cleaner yielded good results. Probably couldn't hurt to replace the o-rings while you're in there. It's worth looking into if you have time to dive into it. There are also some tutorials on youtube about how to clean them out using all types of tricks but I haven't tried any of them personally.
 
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pagrey said:
Some people like @Irun have had good luck smoothing out the idle cleaning out their injectors. From what he described just pulling them out and spraying them down with some carb cleaner yielded good results. Probably couldn't hurt to replace the o-rings while you're in there. It's worth looking into if you have time to dive into it. There are also some tutorials on youtube about how to clean them out using all types of tricks but I haven't tried any of them personally.
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Good to know.

I purchased some unused Mopar injectors from another member months back, so I’ll eventually throw those in.
 
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I appreciate all your responses, work week started so I will have lest time to check all this, but this is the best community in the world. I have quite a few things to check and will report back!
 
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After replacing tyranny mount and using a 1inch spacer it have gotten worse, but it's the exhaust that is transferring the rumble all through my frame, goes away with high rpms, comes back at idle and low rpms, plugged cat probably. But I think I'm 99 percent sure! Thank you all for suggestions
 
reconeTJ said:
After replacing tyranny mount and using a 1inch spacer it have gotten worse, but it's the exhaust that is transferring the rumble all through my frame, goes away with high rpms, comes back at idle and low rpms, plugged cat probably. But I think I'm 99 percent sure! Thank you all for suggestions
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Did you use a MOPAR transmission mount? I had way more vibes in my first TJ after throwing in a cheap Anchor mount from amazon. OEM is the way to go if you want to reduce/limit vibes.

Is your exhaust touching anywhere like your transmission?

A clogged cat can cause other issues like not wanting to go over 50mph. Do you have this additional symptom?

Side note: I've had vibrations when warmed up in idle that did not pop a CEL (with new pre-cats and the third cat removed). I recently drove about 150 miles with 8oz. of Seafoam in the engine oil before changing my oil in hopes to solve a potential sticky lifter noise that happened upon startup about once a month. To my surprise, the shaking is greatly reduced (as in there basically aren't any vibes now when sitting in gear at a light). Just throwing that out there in case nothing else helps solve your issue. Time will tell if my potential sticky-lifter noise is also solved.
 
WestCoastDan said:
I can tell you that when the O2 sensor recently went out on our '03 4.0, the idle was rough...
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I tried that and it didn’t fix my issue, but I consider 02 sensors to be a cheap enough part to change and it’s worth it to me knowing I have a new known good part in for the long haul.

For issues where the Cat simply isn’t splitting the atoms any longer (due to the platinum group metals inside degrading) ,I had great luck (the one time I tried it) by eliminating the CEL by installing a spark plug defouler as a coupler for the down stream 02 on the bank that caused the CEL. This isn’t OP’s problem but I’m throwing it out there in case it can help someone at some point. Saved me a good chunk of $$$ by not needing to purchase a new cat.

EDIT: This would only work for downstream sensors where you want the upstream & downstream to read differently. If your cat doesn't do its job the upstream and downstream 02s will read the same voltage and will pop a CEL. The coupler pulls the downstream out of the exhaust flow enough to cause the 02 to read differently than that upstream. I've only tried this once and it worked to my joy and amazement.
 
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pagrey said:
Which sensor? Did you get a code, replace them all or just one? Just curious after seeing your post, nothing more than that, makes sense to me.
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NTK 23138 Oxygen Sensor; I think it was bank 1 downstream, IIRC…
I just replaced the 1 sensor & it cleared the preheat code that came up.
 
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