How do I diagnose Codes P0171 and P0174 at same time?
What is your question?
I started simple with check for clean air filter, I cleaned the MAF, I checked for vacuum leaks. I believe the O2 sensors are fine as I replaced them about a year ago. I have seen that it may be the fuel pressure causing the issue. Is that the next logical step or should I check something else?
What makes this problem better or worse?
Usually runs fine, sometimes it is a bit rough at idle.
How long has your 2004 Toyota Sienna had this problem?
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Hello, when you have both engine "banks" showing lean, as with this two codes, it's almost always related to an air intake issue - such as a vacuum leak or intake manifold leak. Unmetered air is getting into the engine causing there to be never enough fuel. I'd find it extremely rare to consider fuel delivery an issue with this vehicle.
One known failure is illustrated by a technical service bulletin from Toyota which shows that the intake air control valve number 2 could have a vacuum leak. There is a test procedure to see if this is the case - but this is one possible cause of concern.
Hands on testing is needed to figure out what is going on.
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