Intermittent CEL PO171 &174

2005 v6 tacoma. Have been plagued for month's with intermittent CEL light that no dealership could trace or cure. Symptoms include very rough idle when hot and not moving, erratic take off from stop sign and even dying one time and reluctantly starting. $180 for bank one sensors and much pain installing the one closest to the firewall--- wrong wild ass guess. One dealer said it was due to the gasket for the mass air flow sensor, so they installed a new one -reset CEL. Made 30 miles before CEL reappeared. New stealership checked fuel pressure and it was 35 and should be around 41. They had no parts and $980 installed for fuel pump seems bloated. nice website.

 

P0171 and P0174 are for fuel system lean. That means the computer is reading the incorrect level of oxygen content in the exhaust. Since it is BOTH banks that are affected, the highest probable cause is a vacuum leak. This is not a guarantee mind you, but the highest likelihood. The only way to properly diagnose these codes is to know what the actual readings are for both banks, short term AND long term. Without that information you will be just throwing parts and hoping to get lucky. Can you get this data?

 

Have records of five different CEL.
1 2 3 4 5
STfuel trim 3.1 (.8) 0 7.0 3.9
st fuel tr2 3.9 0 0 (.8) 3.9

ltfueltri 37.5 37.5 35.2 36.7 35.2
ltfueltri 2 35.9 35.2 31.3 39.1 29.7

 

Short term fuel trim is not really the numbers to concern yourself with. They are a quick response to current stimuli. The Long Term is where the information is at unless you are doing active testing. Numbers that high on your long term trim are SCREAMING vacuum leak as a likely cause.

That being said, a vacuum leak can be internal or external. An example of an internal vacuum leak is a stuck EGR valve. (While this would not typically cause a fuel trim lean condition, it can affect the calculations due to the fact that a leaking EGR valve allows unmetered air into the engine) Also a bad PCV valve can cause erratic fuel trim as this is also unmetered air. Basically ANY air that enters the cylinder that is not either expected (In the case of a properly operating PCV valve, or EGR valve) or measured by the MAF sensor, is considered unmetered, and a possible source of incorrect fuel trim readings.

 

If you haven't already tried it, you might clean your MAF sensor, using special MAF sensor cleaner.

Are you running a TRD, K&N or other washable filter?

 

I had the same problem with my 2005.
I changed the MAF and the dealer diagnosis "twice" was the fuel ratio sensors.
The problem is the fuel pump!!!!!
The real problem is the filter/screen attached to the pump,its flat and small.
I don't know if you can just buy the screen.
I bought a denso fuel pump kit from advance auto parts for just over $100.00,its a pump and filter. Easy to change.

 

Would probably get more personal responses in the 2nd gen forum.. Though bamaboy is a guru of excellence

 

Thanks Mark. Gonna do it.

 

Mine did the same over the weekend. I think it is the pump. But after doing all the routine changes. I'm seemingly back to normal. I will drop the fuel tank and swap out the pump just to be sure. I mean, It has a little over 135k on it with no filter change or pump.

 

Reason I found this thread was I decided to search some more.