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2003 Yukon XL 5.3L rough idle: codes P0101, P0171, P0174

ebk

By ebk
in Ask A GM Technician

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ebk Enthusiast

ebk

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Hi everyone,

 

I am new to this forum. I have a 2003 Yukon XL (TK15906 L59 M30). I am trying to do more of the work so that I can afford to keep it. It's great to have access to expert advice in this forum.

 

I am having trouble with a rough idle and it is throwing the following codes consistently: P0101, P0171, P0174 Check engine light is on and it won't pass inspection, which is now overdue. I replaced the MAF sensor with a new Delhi unit. Same codes. I checked all vacuum lines, which seem to be solid. I checked the PCV valve, which doesn't seem to be a valve at all, i.e., no moving parts inside and I can see right through it. I have not had any other codes, e.g., O2 sensor, MAP, etc.. I checked the vacuum using the PCV hose and it reads around 16 mm hg at idle. I am thinking that this is low, but I cannot find a specific leak location. I plan on replacing the intake manifold gasket, unless you have any other suggestions. I will defer to the experts.

 

Thank you for your help!

 

 

 

ebk Enthusiast

ebk

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Thank you! I will try the filter and get you a pressure reading. Is there a way to tell if the regulator is bad (assuming it's the fuel injector pressure regulator)? Also, I have never had a problem getting it to start right away.

ebk Enthusiast

ebk

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No tool yet to measure the pressure. However, I removed the vacuum line from the regulator and no fuel came out, i.e., the diaphragm in the regulator is intact. I also checked the tightness of the intake manifold bolts and some were loose. I tightened them up to 89 in lb and the vacuum increased from 15 (cold) to 18 mm hg. It idled much smoother. However, I am concerned now about the manifold distorting. So, the question at hand is; leave it as it is or take the manifold off and replace the gasket? Also, how often do the injector o-rings leak at the manifold? Now would be a good time to replace them. Let me know your thoughts. Thanks!

txab Senior Enthusiast

txab

Posted
Posted

Replace the intake gaskets. Injector o rings should be fine if they are not disturbed. No need to remove them when replacing intake gaskets

ebk Enthusiast

ebk

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Obvious leaks at multiple locations where the manifold gasket failed. Runs very smooth now at idle and otherwise. Went with a metal vs. plastic backed gasket as well as a new throttle body gasket. I understand how the leak resulted in the lean codes. However, I don't understand how it triggered the MAF code. Too much air for it to compensate? It seems like a pretty common problem and I can see why after taking a close look at that manifold and OE gasket. Thanks again for your help and advice!

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