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.

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.

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.