Check Engine Light Code P0171..
 

The Code P0171 popped on my 2004 Scion has 149,000 miles. I cleaned the the mass air flow sensor. I even swaped it out for the exact same one from my 2012 Tacoma and the code still popped.

I changed the air filter and and checked for any leaks coming from the hoses on my air intake box. the code keeps coming back???? and ideas???

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Vacuum leak, lazy o2 sensor, fuel pressure, etc. Any other codes coming up with the P0171? Do you have any aftermarket parts or running any tunes?

p0171
 

No after market parts. No other codes. I have tried a few things. changed the air filter. cleaned the mass airflow sensor, even swaped it out with the one from my truck. Each time I tried something I pulled the EFI fuse to reset the check engine light, and each time it came back. I've been told that pulling the EFI fuse will not erase the code from the computer so the light will come back on anyway.... I was told to try disconnecting the battery and that should erase the code???? any feed back on this. Also I've noticed that the light only comes on when I come to a stop, and sometimes it feels like it wants to die when its idling. The car does have a sounds system. A kicker amp with 1 12" subwoofer, nothing fancy.

An update. last night I added zip ties to my vacuum line. this morning the car ran like a champ. idled perfect and ran great with no light for about fifty miles. I parked and came back to the car 10 mins later, drove a quarter mile stopped and the light came back on??????

Is it the same code? May have another vacuum leak somewhere....

This is a common issue amongst certain toyotas, I bet your intake manifold gasket is cracked or something else causing the air to sneak in through the gasket area.

Injector O-rings

i know that at least two of the injector o rings are bad. can this really be a problem?

Most definitely is....

Yep. I'm a little disappointed that you know they are bad and you're trying to replace/repair other things, and didn't even mention that in the first place... oh man...

I replaced all four lower cushion rings on the fuel injectors about a week ago. Cars been running like a champ ever scince. thanks all for the help.

Regardless, very glad to hear.