Another Lean Code Mystery: P0171 & P0174

[PsYcHo_FrEkE]

Sounds to me like the intake O-rings are hard/brittle and
leaking. Especially considering the high miles...

That's where my thought process is going, too. Seems like the problem gets worse as it gets colder. I'm planning on going through all of the vacuum lines as well. I didn't find any leaking, but they're very brittle.

I keep waiting for it to warm up a bit (at least into the 50s) before I do the IM gaskets, but I'm not sure the truck is going to let me wait that long...

 

[admonroy]

Psycho, I have read all the thread since I'm having the same problem on my 98 explorer (vin X), did you check the fuel pressure? I did mine today, and at idle is 28 psi, which according to the manual is bellow the minimum values. I'm thinking that's causing the lean codes. Any ideas?

 

[Dirt n Oil]

Psycho, I have read all the thread since I'm having the same problem on my 98 explorer (vin X), did you check the fuel pressure? I did mine today, and at idle is 28 psi, which according to the manual is bellow the minimum values. I'm thinking that's causing the lean codes. Any ideas?

Was it your fuel pump? What came of the matter?

 

[IceHole]

That's where my thought process is going, too. Seems like the problem gets worse as it gets colder. I'm planning on going through all of the vacuum lines as well. I didn't find any leaking, but they're very brittle.

I keep waiting for it to warm up a bit (at least into the 50s) before I do the IM gaskets, but I'm not sure the truck is going to let me wait that long...

So what happened? Dang, I've done it all and still bank 1 is lean. about ready to use it for target practice

 

[Sager]

Been chasing 171/174 codes on my 98 sohc , that has less than 20k miles on it for a year, replaced pcv, egr, idle air sensor, smoke tested it.
Finally bit the bullet this past weekend and had the intake manifold and a few other upper gaskets replaced.
Now on a cold morning, less than 70f, the engine would surge , spit and sputter on lower rpms, sometimes stall.
This morning was the 1st cold start, 38f outside, and it went directly to about 1250 rpm with remote start, sat there for at least 5 mins before i drove it, and stayed rock solid.
We found the lower intake gaskets, had some dark marks on it, indicating that air had been coming in from the outside.
I think we have nailed it, just thought i'd share..