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Discussion Starter #1
I am looking for some advice on a p0171 check engine light that I have been chasing down for the last month. I have done everything that I can possibly think of including the following:

Smoke test
Checked all vacuum lines
Replaced valve cover gaskets
Replaced pre cat 02 sensor
Checked and rechecked all intake/turbo hoses
Carb cleaner along intake manifold and valve cover

During all of these tests I only found 1 pin hole vac leak at the line that goes from the turbo wastegate tee to the rear exhaust flap. My LTFT readings are high(24%) and drop when I increase the RPM's. Based on internet research this is a tell tale sign of a vac leak.

The only item that I have not done extensive work with is the fuel system. Normally I would put a gauge on the rail and check pressure. I think the HPFP is working fine but I don't know about the fuel pump in the tank. Does anyone know how to test that pump out? Any other suggestions of where to look for either too much air or a fuel restriction?

Another thought is the PCV system built into the top of the valve cover, I popped that cap off and inspected and nothing looked broken or ripped.
 

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There is a fuel rail pressure sensor so the DME can compensate for light pressure changes.
If there is anything from the fuel side, that would be clogged injectors.

Air, most of the components are involved including the intercooler. Any of the air related ducts could give problems in naturally aspirated mode. Oil filler cap leak can cause lean mixture if the CCV is getting bad.

Have you checked / cleaned the MAF?
 

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I have a MAF on order, I have tried to clean it and there was no change. Unplugging the MAF creates no change in the behavior at idle. If the oil cap is cheap enough it might be worth simply replacing.
 
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