2016 LR4 - Rough idle but only when warm; worse when vehicle in reverse

Alchern

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Hello gang, My 2016 LR4 runs very smooth at initial start up and when driving, but after coming off the highway and the vehicle is warmed up, the idle seems rough. It seems especially bad when shifting from drive into reverse - it almost hesitates before moving. It is also slightly noticeable when stopped at a red light, when the Eco auto shut-off is disabled. Timing chains have been replaced, but wasn't noticeable after this was completed 6 months ago.
I do have a GAP tool and the only applicable codes thrown are P0142, P0042, P0055 - all to do with O2 sensor Bank 1 Sensor 3 (downstream). New O2 sensor is ordered but waiting forever for it to come in (I doubt this will make any difference in idle). I'm new to GAP tool - what are the best live values to monitor when I am experiencing the rough idle to give me some potential info about what could be going on? Any help would be greatly appreciated.
 

Salanizi

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I had exactly the same issue

Turned out to be the brake vacuum lines leaking and tripping the O2 sensors (engine fuel mix too lean)

It was more prevalent in reverse due to applying the brakes more

Changed all 3 and got it fixed
 

jlglr4

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I think you are on the right track with replacing the O2 sensor, and it very well might fix the idle. In the meantime, you can check fuel trims at idle and at higher RPMs. Look at short term and long term fuel trims once the engine is warm - add them together to get actual fuel trim numbers. Check at idle and at steady 1500 and 2500 rpms (in park, no load). If the O2 sensors are not reading correctly, it will probably fool the motor into running rich or lean, which is what changes the idle speed and gives hesitation. Generally it’s the first pair of sensors that is most important rather than the third pair, but there is likely some feedback from all three.

The reason you don’t see any issues at initial startup is that the car runs in open loop until it’s warm enough. When you run in open loop, the air/fuel ratios are fixed - they don’t change based on O2 sensor feedback. But once the engine is warm, the air/fuel ratios are determined by closed-loop feedback based on the O2 sensor readings.

After you replace the O2 sensor, run your fuel trims again - make sure they looking good and that a rich/lean condition is not persisting - which could actually be the cause of the O2 sensor failing (though more likely the O2 sensor just wore out).

Good luck - keep us posted.
 

Salanizi

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Hello gang, My 2016 LR4 runs very smooth at initial start up and when driving, but after coming off the highway and the vehicle is warmed up, the idle seems rough. It seems especially bad when shifting from drive into reverse - it almost hesitates before moving. It is also slightly noticeable when stopped at a red light, when the Eco auto shut-off is disabled. Timing chains have been replaced, but wasn't noticeable after this was completed 6 months ago.
I do have a GAP tool and the only applicable codes thrown are P0142, P0042, P0055 - all to do with O2 sensor Bank 1 Sensor 3 (downstream). New O2 sensor is ordered but waiting forever for it to come in (I doubt this will make any difference in idle). I'm new to GAP tool - what are the best live values to monitor when I am experiencing the rough idle to give me some potential info about what could be going on? Any help would be greatly appreciated.

Hello Sir

Any chance you got this fixed? I am currently having the exact symptoms u had in your car
 

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