I know this thread is already been talked about but can't find it . Ok the problem is on 5.4 2 valve 130k. When it gets cold outside the Rpms will fluctuate up and down pretty bad ok and other times when it finally starts idling normal it will stall. This only happens when it's cold and it is throwing both lean codes. I've tried cleaning mass air flow, iac, replaced pcv valve, and checked for vaccum leaks. As I don't have a whole lot of money to just start throwing parts at it I was seeing if someone has had the same problem and can point me in the right direction. Thanks

 

There is a temp sensor that tells the computer to make the gas mixture richer. That would be my wild guess.

 

What EXACT codes by number, please? Have you checked the PCV elbow behind the intake for rot and holes?

 

P0171 and p0174 I believe is right and yes I have checked pcv behind intake.

 

Your codes are telling you the engine is getting excess air into the intake tract causing a Lean condition both banks.
This causes the computer to richen the fuel to account for the extra air and sets the codes and causes poor drivability.
You have an air leak to find.
The PCV hose attachment to the intake very often is the cause .
It goes soft from the fumes, then the engine vacuum sucks a hole in, that allows outside air to enter the intake.
Go over all the rubber to and from the intake manifold areas with you hands and inspect well, not just look at them.
Good luck.

 

Ok thanks il try and let you guys know if I find it.

 

Ok so I tried looking for vacuum leaks everywhere and can't seem to find any like I said it only does it when it's cold so could it be either the maf sensor or just a bad iac valve thanks

 

I a 65% sure you have a vacuum leak - especially since you indicate that it goes away when it warms up. Do you have a cracked plastic intake manifold? Crack in the air intake tube downstream of the MAF?

 

Il make sure and do another thorough inspection for vacuum leaks today it was in the 50s outside and the truck would idle fine then it would stall

 

Oh forgot to mention seems like after running for a lil while my low end power goes away

 

Those codes indicate too much air, or not enough fuel. Vacuum leak, MAF, or a fuel issue. Get the truck to operating temp, and unplug the MAF.. does the truck die? Does it change the way it runs? If so, the MAF is working. Check fuel pressure at the schrader valve as well. There will be a vacuum diagram under the hood, trace every single hose! You can also use an unlit propane torch, put it everywhere near the vacuum hoses, and intake tract. The RPM will rise if it sucks the propane gas in. You can also do a "Poor mans" smoke test. Make sure the truck is NOT RUNNING, pull the vacuum booster hose, go to the gas station and buy a cigar, puff that baby and blow into the vacuum hose. If you see smoke coming from somewhere, thats your leak!

 

It is a frustrating place to be. Please read through my experience https://www.f150online.com/forums/v8...171-p0174.html
A methodical, calculating approach is the only way you are going to nail down the cause while minimizing money and effort spent/wasted.
Couple additional thoughts:
-Doesn't sound like a fuel delivery issue, right off, since you don't mention high RPM/high demand hesitation or power loss, only bottom end (which is when vacuum should be at its greatest)


-Renting a fuel pressure test kit at your parts store will help you to rule that out
-Poor engine operation at idle, as the others have said, is most indicative of a vacuum leak




This link was also very helpful http://troubleshootmyvehicle.com/for...d-p0174-page-1
If you are dedicated to fixing your vehicle, you absolutely CAN DO IT. Don't give up!

 

are you losing coolant? As someone else mentioned could be cracked intake manifold filling cylinder with coolant.