Hello experts,

I recently bought a 2012 LR4 with 5.0L V8 engine. (102,500 miles) When I bought the car, there was an engine vibration that transfers to the cabin.
I thought I could handle this problem. After I brought the vehicle to my garage, I changed engine oil (+flush), 8 spark plugs, 8 coil packs, air filters, and cleaned MAF, throttle body, fuel injector for basic maintenance. The vibration became smoother than before but still exists. I really need some help!

Here are the main symptoms.
1. When I start the engine, the idle shakes a little at 1200 RPM, and then it becomes stable at 600 RPM.
2. RPM hesitates when accelerating the vehicle.
3. Loss of power and MPG

Today, I found that there is a problem with O2 upstream sensors (sensor 1), both bank 1 and 2. It reads 0 voltage at all times. (hot or cold engine, long or short drive)
Downstream sensors seem fine. They stay between 0.1 ~ 0.9 V.
Should I simply replace the upstream O2 sensors? From the previous owner's maintenance history, he has changed the O2 sensors 2 years ago at 90,000 miles.
It looks like upstream O2 sensors are relatively new. I am afraid that there are other factors that limit the function of those O2 sensors. What should I do?

Any thoughts? I really need your help.
Thank you and appreciate it.

 

Seems unlikely that both o2 sensors go bad at once. They might just be reading a lean condition on both banks. Are there any codes stored? How are the fuel trims? Rail pressure? The one very common problem that will give you a lean condition is a torn PCV diaphragm, and that will affect both banks.

 

I agree. It is hard to go bad both at the same time. Unfortunately, there is no code that came up. No pending also.
I will check the points that you mention. I would need some time to study how to diagnose the fuel trims and rail pressure.
Thanks a lot. I will keep updating the progress.