Engine vibration when at idle

A forum for the Nissan Armada, Infiniti QX56, and beginning in 2014, the Infiniti QX80
ideffects
Posts: 9
Joined: Sat Aug 07, 2010 1:36 am
Car: 2014 Infiniti QX80
2007 Infiniti M35X

Engine vibration when at idle

Postby ideffects » Thu Jun 24, 2021 12:13 pm

Hey all,

I have a 2014 QX80 with about 110k miles that experiences a engine vibration at low RPM and wanted to see if others have experienced similar issues and what was the cause.

I've done a bit of servicing on the vehicle recently hoping it just needed some love but thus far, the vibration continues.
Completed items:
* Walnut blasted intake valves (new intake gaskets used)
* Replaced plugs with OEM
* Replaced fluids in entire drivetrain
* Trans service (cleaned the pan, replaced the filter and replaced the fluid multiple times with OE Type S)
* Used some Lucas fuel injector cleaner
* Some other stuff I'm probably forgetting about

I connected my OBD diag tool and there are no error codes. I did notice a downstream 02 sensor is responding slowly and falls about 0.1v for a while after a manual (2k)RPM change - it slowly recovers and follows the other bank VO. I'm waiting on a new o2 sensor but this got me thinking that perhaps I have a blocked catalytic converter. I just ordered a backpressure tester to verify.

I also noticed that the idle is a bit erratic going from 650~ to 850~ within the course of 30 seconds somewhat continuously. When the idle is in the 650-700 range, the vibration disappears and reappears once the idle is higher. The IAC program was executed after the walnut blasting.

There is no misfire reported. The engine sounds healthy - just loud ticking from the HPFP.

At this point, the only thing I can think of is a blockage in the exhaust or perhaps a MAF sensor but the MAF seems to be responding correctly to RPM change. Again no codes (stored or pending) to indicate any of these issues. It could be motor/trans mounts but since there are moments of no vibration, I doubt this the root cause.

Any additional suggestions of what it could be are greatly appreciated!
Thanks for reading.


ideffects
Posts: 9
Joined: Sat Aug 07, 2010 1:36 am
Car: 2014 Infiniti QX80
2007 Infiniti M35X

Re: Engine vibration when at idle

Postby ideffects » Sat Jun 26, 2021 8:15 pm

For anyone interested, cats checked out fine. Replacement of the down stream 02 sensor did help but still some vibration when the a/c is on and the fan kicks into high speed only.

Possibly either a fan clutch issue, unbalanced fan(looks intact), alternator amperage issue or motor mount.

adamruiz2001
Posts: 5
Joined: Wed Apr 14, 2021 2:31 pm
Car: 2011 QX56

Re: Engine vibration when at idle

Postby adamruiz2001 » Mon Jun 28, 2021 12:05 pm

You say the RPMs are erratic, I wouldn't assume motor mounts would cause this, I would be looking at plugs or coils. You already did plugs, I would inspect your coils, I had 3 bad coils when I had 120K miles on my QX, bought a new set of 8 and motor is smooth again. Mine would only cut under heavy load but felt like the motor had a cam when idling, again, mine was really bad since I had 3 leaking coils.


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