LR4 poor idle with AC in drive

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Braddisco

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Hey everyone, I finally upgraded from decades of D2’s to a 2011 V8 LR4. Great truck, has 160k on it and just about every repair imaginable done, great service history. That said im running into an issue that has almost everyone (LR techs included) scratching their heads. When I start the truck, turn on the AC and don’t drive, the truck idles great, AC blows cool, all sounds/ runs as it should. But once I start driving then come to a stop the engine goes into an idle fit. RPMs go up and down and I start hearing some clatter from the engine. So, I then quick turn the AC off and the truck returns to normal state of healthy idle. Another way to exasperate this is to start the truck with the AC already ON at start, shift into Drive and boom, idle fit, clatter from engine. No warning light are on the tuck. icarsoft LR V2 tool shows no codes. I should mention I replaced the AC compressor as an effort to resolve the issue, made no difference. All tensors, pulleys V fan are good.

I should also mention that at startup the engine make a brief “clatter” sound for a quick second just before it starts. It’s subtle but present on every start. Just at the moment when you typically hear the starter whirl. Not sure if they are related.

Anyone know wanna take a crack at this? Buy ya a beer…..
 

greiswig

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Shooting wildly here...

You said "when you come to a stop." Does it matter whether it's in park or drive when this happens?

Also, have you checked the alternator voltage when this is happening?
 

Braddisco

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@greiswig thanks for the suggestion. I believe it’s the action of moving, higher rpms, to slowing, low/ idle, that makes this happen. Just simply driving for a bit then coming to a stop. Parking brake on or off would not make a difference. Now sitting idle from start, turning ac on and just sitting, I have no issue doing so. It’s seems as though it’s the ac not in sync with the engine via serp belt. Something in that world of thought. I’m tossing a few new fixes at it tomorrow, I’ll chime back in with results.
 

greiswig

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I was referring to the transmission, not the parking brake. And as I said, did you check voltages?
 

jlglr4

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Couple of thoughts: (1) when you are comparing the situation just sitting idle from start vs moving and then stopping, is the car warmed up in both scenarios. If the car is cold, it won’t be in closed-loop fuel control and will behave completely differently as it’s not dynamically adjusting fuel supply; (2) maybe check your short term and long term fuel trims when the idle problem is happening vs when its not. thinking maybe your evap purge valve (they have them on 2011 models?) is opening when you start moving and then not fully closing again causing a fuel mixture problem. Bad purge valve can make a “clicking” sound, but I wouldn’t call it a clatter.
 

Braddisco

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@jlglr4 thanks for you input. So purge valve was replaced and tested. It’s the same warm or cold. I have attached an audio of the truck on startup. The sound we hear on ignition is what we are listening for. On the recording it’s more of a knock, in person it sounds more like a pop, like a popcorn kernel. This is directly related to what’s happening with the AC. Timing chain was just completed before I purchased the truck so sources on my end believe this could be TC related/ cam shaft.

 

jlglr4

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Can’t seem to access the sound file. The one thing that comes to mind with respect to the clatter is the vvt solenoid.
 

Tbh1981

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@greiswig thanks for the suggestion. I believe it’s the action of moving, higher rpms, to slowing, low/ idle, that makes this happen. Just simply driving for a bit then coming to a stop. Parking brake on or off would not make a difference. Now sitting idle from start, turning ac on and just sitting, I have no issue doing so. It’s seems as though it’s the ac not in sync with the engine via serp belt. Something in that world of thought. I’m tossing a few new fixes at it tomorrow, I’ll chime back in with results.
This was my first thought as well. Belt slip, or the pump, or a tensioner pulley being seized might cause the idle to go bonkers as the engine tries to overcome intermittently changing tension on the serp. belt. Of course, that would be the easy solution. Given my recent dive through hard-to-diagnose LR4 problems, having an issue with your engine idle could very well mean you left-rear passenger seatbelt buckle chime is broken, or some other ridiculous, seemingly unrelated thing.

Good luck. Videos help with diagnosis - get you a YouTube channel, record a video of the problem, and post the link to the video on the forums.
 

Braddisco

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@Tbh1981 thanks everyone for your input. I’m going to take the suggestion of YouTube video. Once the weather clears up here I’ll shoot and post. In the meantime myself and another handy Rover shop have a theory that this could be a faulty throttle body. Maybe it’s a malfunctioning unit. I have a used one on the way and will swap it out. It’s also very possible that despite all pulleys spinning well this could be an issue with one of them going bad as you mentioned. Will report back.
 

Braddisco

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Ok, so the truck went to a very reputable indy Land Rover only shop in South Eastern PA. The report back was that the issue is the fuel injector seals. This makes sense as I have confirmation that a not so good shop did the seals when the timing chain was done. I’m assuming that the seals are installed improperly, causing a compression issue. This would also make sense as the sound is focused on the area of the fuel injectors. It almost sounds like popcorn popping. The shop is installing new injectors this week so I will report back with confirmation that this was definitely the issue and is resolved.
 

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