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Hi Tribeca Community-

We have had our 08 Premier for a a few months, I have done some significant work (pulleys/full suspension/some hoses and most fluids). We noticed that whenever it has been running at freeway speeds for about 90 minutes we are a P0174 (lean condition, bank 2). It runs flawlessly despite the code, but obviously cruise control/traction control get switched off when the code occurs.

After a bit of research I found out that the intake manifold gaskets can leak at high mileage, I got a set of fel-pro gaskets and installed them (yes - removing the intake looks like a 5 minute job... it's actually several hours, especially if you do it the way I did without removing any front belt components). The original gaskets weren't hard, but they did appear to have shrunk significantly over the years on the engine side specifically.

My wife is driving the Tribeca from the Bay Area to LA right now... and the code popped up after 90 minutes (keep in mind she is probably going 80mph+ on I5 with AC on as it's central valley heat).

I read somewhere that in addition to intake gaskets, faulty O2 sensors or a bad MAF can be to blame, but as this only happens when the car has been at 80mph for a good 90 minutes I don't know if that makes sense.

I am thinking that this occurs when the exhaust gets really hot and something expands?
Does anybody know which side is bank 1 and which is bank 2?
Any ideas as to what my next steps should be?

-Matt
 

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Facelift (EZ36D, 5EAT TG5D), MY2008, 7seat Limited (no DVD, no NAVI)
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right side are cylinders 1-3-5(bank 1), left side - 2-4-6(bank 2).

personally - I would monitor sensors - like lambda sensors (all four), maf, injection timing and length - in one of those long drives... and see are there really changes which could be interpreted as lean or it is just one of lambda sensors acting up.
 

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2014 Subaru Tribeca
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right side are cylinders 1-3-5(bank 1), left side - 2-4-6(bank 2).

personally - I would monitor sensors - like lambda sensors (all four), maf, injection timing and length - in one of those long drives... and see are there really changes which could be interpreted as lean or it is just one of lambda sensors acting up.
could swap o2 sensors and see if the issue follows the sensor

maf is easy enough to clean

you could also look at the spark plugs to see if any of the cylinders are burning the plugs
 
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