Good afternoon, everyone! I've been fighting with my 2014 L405 Autobiography (5.0L SC) for the past few months, trying to figure out what's causing a persistent P0430 code. Neither I nor the local indie LR specialist shop can figure it out, so I'm hoping the forum members here can point me in the right direction. Here's the story so far...

A few months ago, I was getting both P0420 and P0430 errors. No other error codes were present using my IIDTool. I brought it to an indie LR shop, and they said it was unusual to see both cats fail at only 80k on the odometer, but not unheard of. They kept the car for several days to run diagnostics and a smoke test on the intake. They said everything seemed to be working correctly, reset the ECU, and told me to try a bottle of CataClean to see if that would help clear things up. Unfortunately, both the P0420 and P0430 error codes were back within a week.

Fast forward a few weeks after... My car began to have a pretty rough idle from a cold start, lasting for about a minute. I still didn't see any other codes on the IIDTool, except for seeing a "random misfire" code once. After seeing that, I changed the spark plugs, ignition coils, PCVs, and catalytic converters, as well as cleaning the throttle body and MAF sensors. After all that, the P0420 finally disappeared, but the P0430 will still reappear every few days, and the rough idle on a cold start is still present.

Today, I logged the #1 O2 sensors, #2 O2 sensors, LTFT values, and MAF sensor values during a short drive around town. (The IIDTool wouldn't let me add the #3 O2 sensors. I guess it has a limit of 8 sensors for logging. I'm assuming the #1 sensors are the pre-cat lambdas, the #2 are the mid-cats, and the #3 are the post-cats).

Here's some things I've noticed, but I'm not sure whether they're relevant...

• The LTFT for bank 1 is always between 4% and 8%, while bank 2 is around 0%.
• I had to replace the mid-cat O2 sensor on the driver's side (LHD) because it broke during removal. But the driver's side on a LHD is bank 2, right?
• While watching the mid-cat O2 sensors on the IIDTool, bank 1 remains pretty steady around 0.750V, while bank 2 will often dip down to around 0.300V. Is this normal?
• The MAF reading for bank 1 always reads about 2-4kg/h lower than bank 2. They both go into the supercharger, so this shouldn't make a difference in the air/fuel calculation, right?

This problem is starting to drive me crazy, so any help would be greatly appreciated!

I've attached some graphs of the sensor values from a drive around town today...