Subtle engine shake at idle - probably nothing.

2014 1GFRE 6-speed manual, ~84K miles but it has been doing this since I got the truck about 4 years ago at ~62K miles.

When at warm idle in neutral (obviously,) there is a subtle engine shake that occurs regularly but is syncopated or "off-rhythm," like maybe every 3 or 7 rotations or something like that. It is always present at warm idle, which is 700 rpm +/- 8 rpm for my truck. It's too subtle to capture on camera or via audio. I feel it through the driver's seat. It is definitely not regular or "on rhythm," like, you couldn't tap your foot in time with it. But it's always there, pulsing every second or two "off-beat."

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EDIT, 30 minutes later after starting from cold & getting to fully warm idle at 700 rpm +/- 8 rpm variation, I think this is probably a wild goose chase. No further reading required.

It might just be normal cyclical vibration due to different resonance modes in the vehicle body, tires, and suspension interacting w/ engine rotation. Since I have adjustable-damping FOX shocks and do change the settings, and frequently vary cargo loads by as much as +/- 500 lbs, these variations would certainly affect the overall vehicle resonance response, making mild & normal idle-engine body shake slightly more noticeable at some times vs. other times.
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Nothing else is wrong w/ the truck that I'm aware of. Doesn't burn oil, no strange sounds from engine, no loss of coolant, etc. No codes related to this or any other issues.

I'm thinking the most-likely culprit would be either a slightly-clogged or weak injector, or maybe a slightly weak coil (if there is such a thing -- can coils gradually lose electrical performance without failing?)

About 5K miles ago I did a 15-minute Berrymans Chemtool B-12 rundown (where you clean the injectors in place by running about a quart or so of pure Berryman's injector cleaner through them with the special hanging pressure-fed rig) but this did not make any difference.

Spark plugs were also all changed at around 68K miles w/ factory spec Densos. No change to the issue.

Also, last time I cleaned the TB and the MAF, & reset the fuel trims by disconnecting the battery for >30 seconds, it also didn't make any difference or change to this subtle shake at idle.

Any other ideas?

 

From what I've seen, most people experience a low idle in Drive and Reverse, with the RPMs going back up to normal range in N and P.

I've never seen a fix for that.

Seems you have the reverse, with the RPMs dropping low while idling in N (and Park?)
How low do the RPMs get when you experience this low idle?

 

@TacoDell60, it's a manual transmission.

The problem is not "low idle," it's a subtle engine shake that only occurs (or is noticeable to me anyway,) at low idle.

The idle rpm is normal and robust, around 650-700 rpm.

 

What RPM range are you seeing when you're feeling the rough idle? I'm willing to bet it's idling lower than it should be while in gear.

 

Again, this is a manual transmission truck, so there is no such thing as idling "in gear." The manual transmission is in neutral when idling.

I will check the idle RPM with a scan tool at my next opportunity, I do agree that it's possible maybe the idle is just set a bit too low. (Though I have never had a problem w/ the truck choking out or stuttering / shutting off at idle, not even once.)

 

Scantool screen captures. Everything looks fine and normal.

 

Mine idles around 750 hot no load and around 750-800 with the A/C on.

Ignition misfires like from a failing coil or spark "leaking" typically show up more under high load than at idle because as compression goes up so does the required voltage for the spark to jump the gap.

That's probably not gona be an easy one to diagnose without being hands-on, did this just start or has it been getting worse?

 

See my edited response in my original post. I think this is probably just normal vibration and I'm having a little bout of Tacoma hypochondria.

I have noticed this mild idle shake since I got the truck ~26K miles ago.

 

Ok lol, mine idles perfectly smooth but it's all stock aside from Magnaflow exhaust and OTT tune.

 

I think to have a chance at tracking down such a subtle complaint (most people probably wouldn't even notice it,) I would probably need to set up an oscilloscope & do a variety of checks like a relative compression test, per-injector electrical current measurement, etc.

I have a Rigol 4-channel scope now but haven't yet got the isolation leads I would need to do some of these tests. If / when I do them I will update this thread.

 

Hmmm FWIW I forgot to mention, I do have the OTT tune installed. I can't recall whether this subtle idle vibe changed at all after installing the tune >10K miles ago. Intake/exhaust etc. are otherwise stock.

 

It's probably doing a evap purge cycle.

Next time you feel it, pop the hood and touch the purge valve, it'll probably be softly tapping away..

Normal