The truck runs fine but if i stop at a red light the rpms will drop for a sec them come back. So i took it to autozone and it pulled both bank 1 and bank 2 02's are too lean. He said i should replace both 02's or its the maff dose this sound right? or what do you think should be replaced. Thanx alot

codes:
P0171
p0174

 

Might be the MAF (clean it), very unlikely it's an O2, MOST likely a major vacuum leak, check the PCV elbow back by the firewall.

For any further assistance, we need to know year and engine.

 

98 5.4 f150 sorry

 

https://www.f150online.com/forums/sh...d.php?t=321963

PCV elbow is the most common cause.

 

ok i just cranked it up the morning everything is fine then it heats up and it starts. The rmps drop and it kind of sounds like it has a bigger cam?????

 

cant really do anything to it right now its 15 degs and ice/snow storm question Why would it only do it once it heats up?

 

The temp change may be expanding the crack or split in a vacuum line. When it is cold it shrinks and seals up.

Regards

Jean Marc Chartier

 

can anyone explain where it is on the 5.4?

 

there is a pcv tube on your passenger side valve cover that goes back to the rear of the intake where it is prone to crack on that bend. check that. if it seems fine replace your fuel filter. a lean condition means either too much air or not enough fuel. the guy who is telling you to replace your 02 sensors is an idiot.

 

Yeah i cant get my hand back to get to it LOL

 

yeah it was a guy at auto zone . The scanner said that too LOL or the maf.

 

mine is fine then the idle will drop/stumble for about 5 sec then go back to normal for a few secs then do it again!

 

i agree with the fuel filter/regulator - might even be the pump. hell , it could be the club combo - worn plugs, packed ports, dirty maf , leaky lines, wheres the air intake, franked up egr, tater up your tailpipe. you won't know until yuh throw a few layers on and have at it.

i think it might be fuel related.

good luck.

 

It sounds like it is on the air metering side....vac leak, contaminated MAF. Definitely check all the vac lines first....you can pull the air box open and see the hot wires on the MAF, look for any debris, trash, etc....if none is found unhook the battery and get some throttle body cleaner and give it few shots, let it dry before starting it again.....having the battery unhooked will clear your codes and it will take two drive cycles for them to set again if you have a problem still. Fuel delivery will set lean codes but you will typically feel a hard stumble with a loss of fuel pressure severe enough to set both banks lean. A new fuel filter is always a good idea though if you are uncertain of when it was changed last.

 

Same exact type of thing happened to me, just found out it is an intake gasket leak. $1k repair from Ford, or a couple hundred in parts if you do it yourself. Hope for your sake it is just the PCV elbow as everyone has stated before.