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Have a 08 jk I've had a problem with it running lean for a few months now. Been to the shop with it 3 times now and still throwing lean codes p1071-p1074 no one can seem to find a problem. Put new O2 Sencers in it have had it smoke tested and fuel and exhaust tested computer flashed. Anyone with a 08 jk been through this before if so what did you have to do to fix it check engine light stills comes on. I still have a slite rattle now and then and stalls out when you come to a stop sign every now and then. Ready to pull my hair out!!!
 

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For lean conditions, conventional wisdom is that there may an air leak somewhere in the air intake path. Could be a vacuum line(s) or even an intake manifold leak. There are lots of videos on YouTube that show how to check.

Good luck!
 

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Check your exhaust manifolds...guarantee you have a/or crack(ed) manifold(s). The 3.8L is notorious for crack manifolds...it was the case why my 08JKU was running lean and my drivers side 02 sensor code popping up and getting shitty mileage. It was a cracked drivers side manifold. Replaced it and it's been running good.

To check just remove the 2 bolts holding the heat shield and you should get a good look of the manifold. I didn't tackle replacing the manifold myself as I was worried about snapping the manifold bolts and got a local shop to do that.
 
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