Hello all, I recently did a ton of repairs to my 2015 LR4 and after 2 months, I'm still having a rough idle that does not seem to go away. Here's a little background on what I have had done recently. Engine is the SCV6.
All started from blown head gaskets that I drove on for about 8 months. (Wanted to believe that it wasn't blown until systems started to fail.)
Replaced Head gaskets.
New Parts Deep Engine: Exhaust Valves, Valve seals, Timing Chains, chain tensioners, chain guides, Bank 1 Intake VVT gear, Bank 1 Intake Camshaft Position Sensor, rotated the VVT sensors and MAFs for good measure.
New Parts External: Cylinder 3,5,6 injectors (Serviced the rest), 3,5,6 Coil packs (Tested the rest), about 8 coolant hoses, thermostat with housing, radiator, water pump, valve cover gaskets, Super charger gasket, intake and exhaust manifold gaskets, Oil Fill cap with O-Ring, Full electrical system check, (Twice) Smoke test for vacuum leaks (Twice), ECU full hardware check.
After all was done (2 months and 2 separate shops later) still having a rough idle that often brings a fault code for bank 2 random misfire 4-5-6. After driving at low speed it will bring a fault, C0700 because the idle is so rough that the oil pressure drops enough to stop the VVT gears and triggers a constant misfire. I shut the engine off, start again and all is fine.
I have a scanner and am seeing the Long Term fuel trim is always 10% lower in bank 2. Even while at speed. No codes from the O2 sensors though.
The last thing that did recently was replace the oil fill camp with O-ring. The idle is a little more constant, and the long term fuel trim is about 7% lower in bank 2, but never goes above %-1.0. Never rich.
1. Could there be another vacuum leak somewhere?
2. Could the timing be off, even though I have had it set 3 times by 2 different shops.
3. Could there be another underlying issue that I am not thinking about.
I am open to suggestions. I am so tired of dealing with this car, but I still like to drive it. I have been searching though these forums for weeks trying to find a hint of what to fix next.

 

You said the timing was set 3 times by 2 shops. Was it off each time, or dud you mean it was checked? If the timing was off each time, that would be significant.

 

The timing was completely off multiple times. The first time was to replace the head Gaskets, chains and tensioners. (First Shop) The second time was to replace faulty new chain tensioners. (Second Shop) The third time to replace a faulty VVT gear. (Second Shop) Only after the third time was this problem of the bank 2 random misfire present.

 

Hello,
Just wondering if you ever solved the issue. I have the same exact issue on the same exact LR4. I stop and turn it off and immediately restart it is fine. Sometimes for days or weeks unless I drive a rough road then it does it constant until I return too smooth roads then it is fine again.

 

Unfortunatly the issue of a random misfire is still plaguing me. Just less often as before. After 50 smoke tests, replacing every seal and plastic part in and around the engine, and every electrical diagnostic test, it will still pop a constant misfire if i feather the gas at about 1200 rpm. It seems to only happen while i am on a bumpy road though. A technician friend of mine said it could be a short in the engine wiring harness, or a back pressure issue in the cats. Both are overly expensive to replace, so i am just driving it until it eather blows up, or i total it on the highway.

if you manage to track down the fault in your system, please post your findings. Thanks.

 

That's where I've been leaning was an issue in the wiring itself or ground because I can even drive for months with no rough running but if I drive a dirt road it will only go about 50 or 100 yards and it starts in. But even then the stop and restart cures it. The upside to that is it is easy to see if any of my attempts change anything. lol I have an '01 Duramax that from the factory the main engine plug had a couple of the pins that would not snap in and hold so they would push back when plugged in and make intermittent contact so it makes me wonder if it is something similar or maybe soldering issues in the ECM.I also have the issue of it killing post cat O2 sensor. I had the dealer reflash the ECM software which was supposed to fix that according to a TSB. It did not. It's my wife's rig and since she doesn't have to work on it she's refuses to get rid of it. So I adjusted the steering wheel for my setting to cover the engine light and have resigned myself to the same thing and just drive it until it dies or kills itself. lol But it's become the idea of the thing and I'm not sure I can let it go. Given what it does on the dirt road it seems it would be simple to find.Thanks for the response. Should I finally find it I'll let you know.