Pontiac GTO 2004-2006 - Lean Codes P0171 and P0174

I keep getting these on and off on the GTO.... Sometimes they go away before I can even reset it (a few starts). I have been trying to figure out why and I am starting to get VERY frustrated. Between each step I would clear the code and wait for it to come back, and every time the amount of time varies.

First I cleaned the MAF (paper filter) and checked that the intake pipes were sealed.

Next I checked my PCV hoses and put clamps on them because they were not clamped.

Next I pulled the TB and checked the gasket, looked good, reinstalled.

Today I pulled the manifold and changed the gaskets... and it came back.

What's left other than a bad MAF?

Thanks in advance for the help,

John

Also, car runs great. STFTs at idle look fine, but the LTFTs are very high, like pegged at 25%.

MAF reads .8 lbs per minute or just under at idle. MAP is reading about 4.5.

I cannot log, just scan... I know lame. MAF is OEM.

Vacuum leak?

That is what everyone says. I just cannot find the damn thing.

LTFTs are high 20-25 at idle and a consistent 2500 rpms. STFTs look okay. OEM MAF reads .8 lbs per minute or just under at idle. MAP is reading about 4.5. BARO is 14.5 PSI and car shows 4.5 which is spot on for good vacuum based on what I have read. Also the MAF seems to be reading in the accepted range, albeit the bottom of it.

I am thinking I have a vacuum leak in a piece of tubing..?

Did you figure this out? My car is doing the same.

I had the identical problem, including the same codes and high fuel trim readings. Turned out to be a bad wire in my MAF connector.

I had a similar problem and it turned out my intake manifold had a manufacturing defect and had cracked at the back where the vacuum lines attach.

I had a similar problem and it turned out my intake manifold had a manufacturing defect and had cracked at the back where the vacuum lines attach.

Were your LTFT's pegged at +25% or just too high? Over time I've been progressively been increasing my slope on the injectors to compensate for lean codes. I'm at 18% and holding for now. I expect this continue, I was going to pull the O2 sensors around the cats and replace them as I searched high and low for a leak.

Yes my LTFTs were high and the exhaust smelled really rich. It also had a tendency for the idle to bounce up to 1500 rpms while sitting at stoplights. It was very frustrating and we only found the leak when my tuner hooked a smoke machine up to the intake manifold. Then the leak was very evident. A little plastic welding fixed it.