System too lean at idle - Bank 1 and 2

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loowee

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Hey guys ! Been having some strange behavior when start the LR4 for over a week. When truck has been sitting for an hour or more ( engine cold ), the RPM will go up to 4500x for the warm up instead of sitting in the 1500x range as it should.

This is probably very bad for the engine as it revs very fast right on start. After the warm up, rpm goes back to normal and truck runs relatively fine but I noticed it stutters a bit and idle varies in the 1000s.

ObdII gives me the following errors on both banks. I resetted the error codes and they came back right away.
My local mechanic tells me he cant do anything since its most likely an electronic or software issue. He tells me something is wrong with the cylinder firing as well and this is probably the cause of the stutters so I might have 2 issues.

The truck is 2014 and has over 200 000kms. Closest dealer is 10 hours away. Truck runs fine once hot and if I stop engine and start again right away, it does not do the high rpm startup thing.

I am scared of using it and damage the engine but I need to get it back on the road asap as it is my main vehicle.

See obdII diag codes below. Any tips or insight is appreciated.
1000016590.jpg

Thank you !
 

djkaosone

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Have you tried replacing both MAFs? The MAFs will affect fuel trims. What are the STFT and LTFT on both banks?
 

alldazed

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If it was me I’d try cleaning both maf’s with the MAF specific spray cleaner. You could also switch them over and see if the problem changes from one side to the other if the spray doesn’t help. Note that it won’t affect banks by switching them over as each MAF feeds from each air cleaner and they both feed the single throttle body . I cleaned mine up over a year ago after the check engine light was triggered and it went away until a week or so ago. I could feel a slight hesitation at partial load so I cleaned them again and put in new air filters at the same time. Been good again.
 

jlglr4

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Sounds like one fantastic mechanic you’ve got there. MAF code would suggest the MAF as the other say here. Try cleaning. If the code persists, try swapping. If it follows - replace that MAF. If it doesn’t follow but persists on that same bank. Might be wiring harness to the MAF.

Also could be a vacuum leak someplace between the MAF and the cylinder. Most common is the PCV valve diaphragm. Pretty easy repair, though a little tougher to get to with the supercharger. Also, breather tube on the drivers side of the engine sometimes gets knocked off the air intake plenum (this happened to me).

Running really lean like you are right now will cause some rough running at idle. That doesn’t mean you have a separate problem (necessarily). I think if you fix the lean condition, you’ll probably be fine.

When your engine is cold, it’s in open loop fuel control (running on scheduled fuel delivery without a feedback loop). Once it warms up, it goes into closed-loop fuel control, where your O2 sensors are telling your engine to adjust fuel because the ratio is not right. That’s probably why it’s behaving differently once it warms up - it’s trying to balance out the lean condition.
 

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