LTG running lean at idle

I have a P0171 on my '14 CTS 2.0T (55k miles), and the LT fuel trim is like 30 or more while the ST is minimal of course
first thing I checked was if it improved while revving up to 2k RPM to see if it could be a vacuum leak which is common
does not improve at all as a matter of fact got a little worse (almost positive 40 lean LT fuel trim) making me thing it could be a fuel delivery issue
low side fuel pressure is about 58 psi (normal no?) and high side around 280+ (but it equals the desired)
oxygen sensor is switching normally, I cleaned and disconnected the MAF and no change
injector balance test all 4 equal (about 63-65 psi drop)
there are no additional codes
I checked the vacuum lines in the motor mounts as it does have a shaky idle (no misfires though)
but again trims do not change off idle
I even removed the air filter and cleaned the throttle body then drove it,
still no matter what LT fuel trim climbs to 30-40 lean after I reset it no matter what
Any thoughts?

Post a data log.
Best guess is you have an air leak , either on the induction or exhaust side.

If you don't have a vacuum leak it could be a bad upstream 02.
I've seen this when the upstream O2 was bad. Kept telling the ECM the mixture was rich when in fact it was perfect. So the ECM kept pulling fuel, resulting in a lean mix.

Another time I've seen this, the gasoline had too much Ethanol and the car didn't have a Flexfuel sensor. Anything higher than 15% Ethanol will do this. Sometimes even 15% could do it in very cold weather. The cts 2.0 LGT recommends Premium 91+ octane which should have next to no ethanol. But you can safely run Regular gas as long as it doesn't have more than 10% ethanol.

I came across this video on how to diagnose 02's with lean or rich condition.

I've not seen a better video explaining 02's and diagnosing lean/rich conditions.

https://www.youtube.com/watch?v=Dwij_fuceUo&t=199s

Quote:

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Originally Posted by ZeroBoostBuick

I came across this video on how to diagnose 02's with lean or rich condition.

I've not seen a better video explaining 02's and diagnosing lean/rich conditions.

https://www.youtube.com/watch?v=Dwij_fuceUo&t=199s

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Thank you Zero

I ended up putting a new high pressure pump in it and a new PCV pipe (was dry and cracked while testing) and the trims improved from 30-40 to 15. Still a mystery to me but car left with no check engine light. I think it sets 171 at 25 trim

Quote:

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Originally Posted by TurboCobalt

Post a data log.
Best guess is you have an air leak , either on the induction or exhaust side.

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Sorry I failed to post a log but I nitrogen smoked the intake system and soap watered the exhaust no indication of leaks visible. Thank you for your time

Quote:

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Originally Posted by ZeroBoostBuick

If you don't have a vacuum leak it could be a bad upstream 02.
I've seen this when the upstream O2 was bad. Kept telling the ECM the mixture was rich when in fact it was perfect. So the ECM kept pulling fuel, resulting in a lean mix.

Another time I've seen this, the gasoline had too much Ethanol and the car didn't have a Flexfuel sensor. Anything higher than 15% Ethanol will do this. Sometimes even 15% could do it in very cold weather. The cts 2.0 LGT recommends Premium 91+ octane which should have next to no ethanol. But you can safely run Regular gas as long as it doesn't have more than 10% ethanol.

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I already swapped the O2 sensor to a known good one and no change. Running unknown fuel I suspect to be pump 87 (E10), I thought of this as well but it's hard to convince people to run premium. LTGs I work on always knock