Codes P0507, P0171 and P0174

IFYUSER

MEMBER
2003 VOLKSWAGEN PASSAT
2.8L
6 CYL
2WD
AUTOMATIC
179,000 MILES

I have a high idle rpm's and lean condition on both banks. The pids for the short fuel trim are positive 25 and long term fuel trim 20 at idle. They decrease when under load. My question is I put smoke through the intake hose and the PCV valve the ones with a diaphragm was leaking smoke. Are they suppose to leak smoke? I read they do cause a lean code on both banks and rough idle, like I get when ever I reset the code until the pids adapt. Or could it be a vacuum leak?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,645 POSTS

Hi,

Any vacuum leak can cause a lean mixture. When unmetered air enters the combustion chamber, the oxygen sensors recognize it and tell the computer to make the fuel mixture richer. Hence, the readings you have on the fuel trims.

Now, I'm not sure exactly what you are referring to as leaking smoke. Can you explain? Also, here is a link that explains how to locate and repair a vacuum leak. Take a look through it and see if it helps.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Now, based on the information you provided, I suspect it is a vacuum leak. If it was being caused by low fuel pressure, and it could be, I don't feel you would have the P0507 which is related to a higher than expected idle speed. A vacuum leak can cause that.

Let me know if this helps or if you have other questions.

Take care,
Joe

Codes P0507, P0171 and P0174

1 Reply

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